Frank B. Cross

“ Both extreme values for the hybrid seem to result from the cumulative influence of characters in which the parental species differ slightly in mean value (especially head-length, in which the hybrid is like whipplei, and caudal peduncle-length, in which the hybrid approaches venustus, despite the 9-rayed anal fin of the hybrid) . The basicaudal spot of the hybrid is like that of N. v. venustus except for being less intense. ”

“ The peritoneum is mottled dark and silvery in the hybrids; it has a composite of the coloration in the parental species rather than a blended shade. The intestine has two diagonal loops crossing the ventral part of the body cavity, and the hindgut lies high in the cavity, along the left side of the air bladder. In Campostoma, the long gut is transversely coiled around the air bladder, whereas in Semotilus the gut forms a longitudinal, flattened, S-shaped loop, ventral to the air bladder. ”

“ Hubbs and Miller (1943:373-374) reported that hybrids of Gila orcutti × Siphateles mohavensis have larger, more robust heads than either of the parental species, perhaps because of heterosis. The enlarged heads in hybrids of C. erythrogaster and N. c. frontalis result primarily from elongation of the postorbital region, with lesser elongation of the snout and orbit. The enlarged head affects measurements obtained for other structures that are parts of the head (and expressed as proportions of standard length or head-length) , causing a tendency toward N. c. ”

“ However, one arch bears only three teeth, all deformed and badly aligned, plus a pit that presumably represents a lost fourth tooth. At the other extreme, one arch bears eight teeth, some of which are attached to the arch between and behind others that are countable as part of the basic main row. ”

“ Specimen No. 4253 is mostly pallid, resembling Gila much more than Rhinichthys in pigmentation. A mid-dorsal dark streak is conspicuous in the hybrid, especially anteriorly, but is less intense than in Gila. Rhinichthys lacks a well-developed dorsal stripe. The preorbital and suborbital areas are more heavily pigmented in the hybrid than in Gila, but not nearly so dark as in Rhinichthys. The hybrid has a faint dark basicaudal spot that is variably developed in Rhinichthys but absent in Gila. ”

“ KU 2947 (28.0 mm. in standard length) from Mill Creek, Wabaunsee Co., Kansas, Sec. 30, T. 12S, R. 9E, Mar. 22, 1953. Compared in Table 2 with five specimens of C. erythrogaster, KU 2836 (27.2 to 31.0 mm., mean 28.5) from the same locality and of the same date as KU 2947 (above) ; and with five specimens of S. atromaculatus, KU 1954, 2499, 2703, and 2838 (25.5 to 31.1 mm., mean 28.9 mm.) from streams in the same area.
This hybrid is intermediate between the two species in number of scales and pharyngeal teeth, and has a composite of the pigmentation found in the parental fishes (Table 2) . ”