FOSSIL FISHES OF THE ENGLISH CHALK. 



Family Cltjpeid/e. 



The only genus of herrings hitherto recognised in the English Chalk belongs to 

 the more primitive section of the family, in which the abdominal border is rounded 

 and covered merely with the ordinary scales. 



Genus SYLL^IMUS, Cope. 



Syllsemus, E. D. Cope, Vert. Cret, Form. West (Eep. U.S. Geol. Surv. Ten-it,, vol. ii, 1875), p. 180. 

 Leptichthys, A. Stewart, Amer. Geol., vol. xxiv, 1899, p. 78. 



Generic Characters. — Trunk subcylindrical, not much laterally compressed; 

 head and opercular region compressed to a sharp edge below. Snout acutely 

 pointed, but not produced ; cranial roof slightly arched from side to side, with a 

 shallow rhombic median depression in the frontal region ; orbit very large, and 

 sclerotic capsule ossified ; cleft of mouth extending beneath the anterior half of 

 the orbit ; maxilla very stout, with a single close series of minute conical teeth ; 

 one slender supramaxilla ; mandible short and deep, with a similar regular series 

 of slightly larger teeth. Preoperculum forming a great triangular expansion, and 

 suboperculum relatively deep. Pectoral fins inserted slightly above the ventral 

 border ; pelvic fins very remote ; dorsal fin imperfectly known, moderately 

 extended, with some of the anterior rays not articulated, but having their right and 

 left halves not fused together; anal fin apparently absent; caudal fin deeply 

 forked, with slender lobes. Scales large, very deeply overlapping, smooth, and not 

 serrated or crenulated on the posterior margin. Lateral line conspicuous, a simple 

 tube piercing all the scales it traverses, arising low down on the flank not far 

 above the pectoral fin. 



Type Species. — Syllsemus latifrons (E. D. Cope, op. cit., 1875, p. 181), from the 

 Upper Cretaceous of Pike's Peak, Colorado, U.S.A. 



Remarks. — This genus lias hitherto been placed in the Percesoces by Cope and 

 the present writer ; but the careful preparation of one specimen in the British 

 Museum has now demonstrated that a precoracoid arch is present in its pectoral 

 girdle, while there can be no longer any doubt that its so-called premaxilla is 

 really a maxilla. The osteology of the fish, as now understood, seems to necessi- 

 tate its reference to tlie Clupeidae, in which family one species has already been 

 placed by Alban Stewart. 1 



Leptichthy8 ayilis, A. Stewart, Univ. Geol. Surv. Kansas, vol. vi, 1901, p. 372, pi. lxxii, fig. 1. 



