Cephalothorax

“ The cephalothorax being united with the abdomen at no great distance from the spinners, the anterior portion of the abdomen, with its appendage, is situated vertically above the thorax. The abdomen is nearly smooth above, and covered with very fine hairs below; it terminates in an obtuse point directed upwards.
Six spinners in a quadrangular group immediately before the vent: the anterior and posterior pair are of moderate size: the third pair is very short, and situated between the posterior spinners. ”

“ Since the above description of the female of this species was written, an example of the adult male has been most opportunely discovered. It is much smaller than the female, its length being only six lines. The Cephalothorax is of an uniform clear yellow-brown colour, tinged with orange, and thinly clothed with a greyish pubescence: the oblique indentations marking the union of the cephalic and thoracic segments are indicated by a strongish black-brown band on either side, which becomes obsolete as each approaches the other near the central curved indentation ”

“ The body of the Eurypterida consists of 18 segments and is functionally divided into two sharply distinct regions, the cephalothorax or prosoma, consisting of six fused segments and the abdomen consisting of 12 segments. The cephalothorax with its appendages is specialized for locomotion and prehension, while the abdomen is essentially a vegetative sac. The six segments of the cephalothorax find their expression in the six pairs of appendages. The cephalothorax consists of the carapace or head shield and the organs of the underside. ”

“ A relatively narrow doublure surrounds with uniform width the frontal and lateral margins of the cephalothorax. The doublure at the base of this shield is three times as wide; it follows the entire posterior margin, thus making the doublure ring complete.
Abdomen. The abdomen widens to the third or fourth dorsal segments, where, in mature individuals, it seems to have been wider by one fourth than the base of the cephalothorax. From this point it tapers very gradually to the telson. ”

“ The abdomen, where the pedicle enters it, gives off a chitinous collar, which projects over the cephalothorax, and has the inner surface of the dorsal part finely toothed. When the abdomen is raised and depressed, these teeth scrape against a number of fine striae on the back of the posterior part of the cephalothorax. A similar organ has been since found in various allied spiders, of which the commonest English species is Steatoda bipunctata. In this group it is generally possessed by the male alone, being merely rudimentary, if present at all, in the female. ”

“ In some species the male presents a remarkable difference from the female in the structure of its cephalothorax, which has the head region produced into eminences sometimes of the oddest conformation. An extreme example is seen in Walckenaera acuminata, a fine species in which the male caput is produced into a sort of spire, bearing the eyes, and nearly as high as the cephalothorax is long (Fig. 209, 3) . ”

“ Cephalothorax: As long as it is broad, upper margin truncate, sides nearly straight, lower margin straight; no suture; four distinct eye spots; eyes on each side almost touch each other.
Abdomen: Elongate, three times as long as it is broad; scuta entire.
Palps: Coxa smooth; trochanter small; femur long, outer edge almost straight, inner edge slightly convex; tibia short and stout, pedicellate, convex on inner and outer surface.
Claw: Not large; finger as long as hand and not curved very much; hand, broad, evenly convex on inner and outer edges. ”

“ The latter are subelliptic, very prominent, project beyond the margin of the carapace and are located at the antelateral angle of the cephalothorax. Their length is nearly one half that of the lateral margin of the cephalothorax; their distance from each other is distinctly less than the length of the eye. As more fully stated in the generic description, the compound eyes are entirely smooth in their exterior view, the facets becoming visible only when the exterior layer of the cornea has become split off or on an interior view. The facets are small and squarish in shape. ”

“ These lines begin behind the extremities of the hinder row of eyes, and gradually converge to a point at the thoracic junction; the ocular region and central longitudinal line of the fore-segment of the caput have some long and very prominent black bristles. When alive, the cephalothorax appears to have been suffused with a purplish hue, corresponding to that of the abdomen and other parts. ”

“ Arachnids with non-chelate, two-jointed chelicerae, powerful pedipalpi, and four pairs of legs, of which only the last three are ambulatory, the first being used as tactile organs. The cephalothorax is usually covered by an undivided carapace, but the pedunculated abdomen is segmented. Respiration is by lung-books. ”

“ Cephalothorax narrow; eye-rows short and far apart; P. M. E. slightly oval, about three diameters apart and much closer to the larger P. S. E.; legs moderately long, very hairy or bristly, and with stout spines especially on femora III and IV; tibiæ I and II with three spines beneath, one at base, one at middle, one at tip, metatarsi with basal spine only; metatarsi and tarsi scopulate beneath; hind legs more numerously spined; sternum once and a half longer than broad, pointed behind, narrowed in front; abdomen fully twice as long as broad, sides subparallel. ”

“ Cephalothorax. Outline of carapace or cephalothoracic shield semielliptic. In the type of the species, the carapace of a young individual, the lateral margins converge but slightly forward; the anterior angles formed by the projecting eyes and the anterior margin being well rounded. In mature carapaces the lateral and anterior margins are less rounded and more nearly straight, the lateral margins subparallel. ”

“ Cephalothorax dull yellowish, a marginal dark seam, eyes on black spots; mandibles dull yellowish. Legs pale yellowish, femora and coxæ more whitish, tibiæ and patellæ I and IV tipped with black. Sternum yellowish, margined with dark. Abdomen above gray, with scattered white spots and larger black patches; a basal black spot each side, and two others each side toward tip, the last larger and extending down on sides to near the spinnerets ”

“ Adult female; length very nearly 14 lines; length of the cephalothorax, 51/2; greatest breadth of ditto, 5; breadth of fore part of caput, 4 lines; length of caput rather over 3 lines.
The cephalothorax of this spider is rather broader in proportion to its length than that of Ct. Sauvagii, Walck., Sim. = Ct. fodiens, Walck. The convexity, or elevation, of the caput is also less, but that of the thorax is greater, so that (when looked at in profile) the profile line of the two forms a tolerably even and continuous slope, interrupted only by the thoracic fovea ”

“ The entire animal is small, but robustly built. The cephalothorax is relatively large, its length equal to that of the preabdomen. The body is sharply divided into the broad, short preabdomen and the narrow, cylindrical postabdomen. While the carapace was slightly elevated, the segments of the preabdomen were strongly arched, increasing in hight posteriorly and the last four segments were circular in section. ”

“ The fifth pair is developed into swimming legs with bladelike and extended seventh and eighth segments. Its ninth segment is rudimentary. The ventral membrane of the cephalothorax is separated by a distinct suture from the doublure of the carapace, but no epistoma is formed. The metastoma is oval in outline, but slightly emarginate in front. The tergites and sternites are more or less bandlike and plain as in other genera; the male opercular appendage is small, with simple median lobe ”

“ The abdomen is large, and somewhat flat with deeply serrated edges, and both it and the cephalothorax, which is slight and to some extent overhung by the abdomen, are whitish or whitish-yellow above and darkly speckled brown and yellow below, while the legs are longish and definitely banded. If she' hung back upwards, the white would betray her, but with the lower side up it is wonderful how inconspicuous she is against the ruddy soil of the karoo. If alarmed she shakes the web until it vibrates with astonishing rapidity, so that she becomes merely a haze ”

“ We have secured little additional material since the Sarle collections were added to the museum and therefore reproduce the original description with our observations appended:
This species is comparatively rare and is not represented in the collection by any entire individuals. There is, however, sufficient material to enable its main features to be correctly determined.
The entire animal is large and robust, and broadest at about the third segment. The cephalothorax is two thirds as long as broad, eyes of medium size, appendages heavy. ”

“ Color: Cephalothorax light reddish brown, pedipalps darker, abdomen and legs pale yellow.
Similar to C. dorsalis, but fingers a little longer than hand; no eye spots, clavate hairs found on all parts of two types, on legs and pedipalps more clavate on one side (Fig. 3) on body evening clavate (Fig. 4) . Simple hairs found on under surface of tarsus. All parts covered with small chiton plates.
Habitat: Specimens taken from under stones in wash near Claremont.
(Contribution from the Zoological Laboratory of Pomona College)
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EXPLANATION OF FIGURES
Figure 1. ”

“ The postabdomen also is relatively wider or stouter than in the older individuals, while on the other hand, the relative lengths of preabdomen, postabdomen and telson to the total length have remained nearly the same. Still younger individuals would surely show other differences in these ratios. The cephalothorax which in our young and old individuals occupies about one sixth of the length and is a relatively insignificant part of the body, compared with the other eurypterids, has most probably lost in relative proportion during ontogenetic development. ”