﻿COSMOPTYCHIUS STRIATUS. 



43 



and the anterior part of the upper margin of the interoperculum ; the branchiostegal rays 

 are numerous, and there is a median plate behind the symphysis of the jaw. The denti- 

 tion of the jaws consists of a row of laniary teeth, conical, sharp, moderate in size and 

 pretty closely set, external to which is a series of still smaller teeth. 



I have instituted this genus for the beautiful fish, from the Wardie Shales, first 

 described by Agassiz as Amblypterus striatus. In general aspect it approaches the next 

 genus, Elonichthys ; but the peculiarly extended base of the ventral fin, as well as the 

 structure of the opercular apparatus, afford perfectly valid marks of distinction. As I am 

 as yet with certainty acquainted only with one species, an enumeration of the generic 

 characters more minute than that given above is not required. 



Cosmoptychius striatus, Agassiz, sp. PL III, figs. 1, 2, 3, 4, 5, 6, 7, 8. 



Amblypterus striatus, Agass. Poissons Foss., vol. 2, pt. 1, p. Ill; Atlas, vol. 2, 

 tab. iv b, figs. 3, 4, 5, aud 6, 1835. 



— — Paterson. Edin. New Philos. Journ., vol. xxiii, p. 153, 1837. 



— — Morris. Catalogue of British Fossils, p. 317, 1854. 



Description. The length of the head is contained five times in the total, four times 

 up to the bifurcation of the caudal fin ; the greatest depth of the body is contained three 

 times from the last-mentioned point to the tip of the snout. The general form of the fish, 

 though rather deep, is not inelegant, as may be seen from the specimen represented in 

 PL I, fig. 1, the most perfect I have ever seen, though the scales of the tail-pedicle are 

 broken up and have almost completely disappeared. It measures 10J inches in length 

 by 2f in depth at the origin of the ventral fins, and most of the specimens seen in 

 collections, usually fragments, entire specimens being very rare, indicate fishes of about 

 that size, though remains of smaller and younger individuals are also not uncommonly 

 met with. The bones of the cranium proper are too much crushed for description ; in 

 PL III, fig. 2, the snout is seen to project over the mouth in a rounded prominence, not far 

 behind which the position of the anteriorly placed orbit is evident. Behind the orbit some 

 of the outer set of suborbitals are visible, though somewhat crushed and broken. The 

 hyomandibular, a portion of which is also seen in fig. 2, is very obliquely placed and is of 

 the usual form. The operculum (op., PL III, fig. 3) is very narrow, its inferior extremity 

 is acuminate, being bevelled off in front to admit of the intercalation between it 

 and the forepart of the upper margin of the interoperculum of a small triangular plate 

 (s. op.), whose upper acute angle is prolonged into a small slender process passing up for 

 some distance along the anterior margin of the operculum, evidently the homologue of 

 the larger plate which in Rhabdolepis (PL II, fig. 6, s. op.) entirely separates the 

 operculum from the interoperculum below. The interoperculum (i. op.) is nearly square- 



