Charles Whitney Gilmore

“ Vertebræ.— The coalesced atlas and axis are very large, and this is the first indi-vidual I have examined which shows the suture separating these vertebræ. (See Fig. 12, S.) On the lower border the atlas is 35 mm. wide antero-posteriorly, the axis being 30 mm. The great disparity in length antero-posteriorly between the Fig. 12. Atlas, axis, third, fourth, fifth, and sixth cervical vertebræ of Baptanodon robustus. ”

“ The centrum is very thin antero-posteriorly and in this respect some-what resembles the corresponding centra in Baptanodon discus. . . . When more material is available it will be interesting to learn. whether this form really repre-sents a true- Ichthyosaurus or possibly a more highly specialized form of Baptanodon than those we know from the Baptanodon beds. Should it be Baptanodon, it will probably show some extreme specializations, as the time separating the Benton from the Baptanodon beds is considerable. ”

“ These missing parts have been restored from the pectoral girdle of B. discus, No. 878 in the Carnegie Museum.
The coracoids are broad subquadrangular bones winch join one another medially by large elliptical facets. The superior surfaces (Plate XXXVIII., Fig. 2) are flat-tened, although both elements are gently inclined toward the median line. The inferior surfaces are concave transversely and convex antero-posteriorly. The lateral borders are especially thickened forming a heavy articular face for the scapulæ and humeri. ”

“ W. J. Holland, [2] the writer was accorded the privilege of studying this specimen, thinking perhaps it would give some information regarding the obscure points in our knowledge of the anatomy of this interesting reptile.
The skeleton like nearly all of the American Jurassic Ichthyosaurians was enclosed in a very hard limestone concretion [3] much seamed and cracked by exposure to the elements. ”

“ There is evidence of the opposite element in a fragmentary posterior end found in the matrix along the other ramus. Otherwise the shape and proportions are very similar to the thyrohyal of No. 878 described and figured previously.
Sclerotic Plates
Although crushing has badly distorted the sclerotic rings of both orbits there appears to be essentially the same number of plates (14) as observed in other members of this genus. The distortion mentioned above has so displaced the plates Fig. 3 Cross-section of the sclerotic plates of Baptanodon natans (No. 1441) . One half natural size. ”

“ Skull of Baptanodon discus. 1, Superior View (No. 878) ; 2, Inferior View (No. 603) . Both 1/5 Natural Size. Some sutures drawn after No. 1441.
EXPLANATION OF PLATE XXXVIII.
1. Anterior view of pectoral girdle of Baptanodon robustus (No. 919) . Type. One fifth natural size, co., coracoids; sc., scapulæ; x., surfaces for attachment of the clavicles.
2. Dorsal view of the same girdle. One fifth natural size. co., coracoids; sc., scapulæ ; x., surfaces for attachment of clavicles.
Pectoral Girdle of Baptanodon robustus (type specimen) . 1, Anterior View ; 2, Dorsal View (No. 919) . ”