BRITISH FOSSILS. 



Decade YIII. Plate Y. 



ISTIONOTUS. Gen. Nov. 



[Genus HISTIONOTU (Isnov, a sail, and vcotos, the back). Egerton. Sub- • 

 kingdom Vertebrata. Class Pisces. Order Goniolepidoti. Family Lepidostei. Sub-family 

 Lepidostei homocerci. 2d Group Body elongated, more or less fusiform.) Dorsal fin 

 commencing behind the nape and extending to the tail ; teeth elongated ; scales serrated, 

 articulated as in Pholidophorus.] 



Histionotus angularis. Sp. Nov. 



Description. — The subject of this article presents a more remark- 

 able combination of characters than any fossil fish with which I am 

 acquainted. It has the head and tail of a Lepidotus, the dorsal fin 

 of an Ophiopsis, the scales characteristic of the genus Pholidophorus 

 and the form of a Semionotus. At the same time it differs so 

 essentially from each of these genera, that it can be assigned to 

 none of them. The generic title I have adopted records its most 

 emblematic feature, the dorsal fin. The specimen figured in the 

 accompanying plate, (the only one of which I am at present cog- 

 nizant, with the exception of an imperfect one in the Museum of 

 Practical Geology,) measures 6 inches from the nose to the com- 

 mencement of the caudal fin, the head occupying about one third 

 of the entire length. The greatest depth, 2^ inches, occurs at the 

 point of commencement of the dorsal fin. The outline of the head 

 very much resembles that of Lepidotus minor in the rapid declina- 

 tion of the frontal bones and the prognathic character of the jaws. 

 The interior of the mouth is not visible ; it is impossible, therefore, 

 to determine whether it was furnished with supplementary teeth, 

 as in Lepidotus and Semionotus, or with a single row, as in Pho- 

 lidophorus. The piincipal series is well displayed ; the teeth com- 

 posing it are very uniform in size and shape ; they are straight 

 elongated cones with blunt apices, and quite smooth on the surface ; 

 nearly resembling the outer teeth in some of the slender-toothed 

 Lepidoti ; the pre-operculum is unusually strong and very rugged 

 [viii. v.] 8 F 



