BlilTISH FOSSILS. 



Decade VIII. Plate YIII. 



PTTCHOLEPIS CURTUS. 



[Genus PTYC HOLE PIS. Agassiz. (Sub kingdom Vertebrata. Class Pisces. Order 

 Goniolepidoti. Family Sauroidei. Sub -family Sauroidei homocerci. 1st Group. Tail 

 forked.) Scales thick, elongated, plicated transversely on the base, and deeply furrowed 

 longitudinally; under-surface smooth, and devoid of rib; pectoral fins pointed; dorsal 

 fin opposite the ventral fins ; anal fin remote.] 



Pti/cholepis curtus^ Sp. Nov. 



Description. — The beautiful little specimen figured in the plate 

 accompanying this description affords another proof (were further 

 evidence requisite) of the value of dermal characters in the deter- 

 mination of fossil fishes, more especially those of the secondary 

 formations, where the internal skeleton is so rarely preserved. Were 

 a mere outline of the fish before us submitted even to Professor 

 Agassiz himself, I very much doubt whether he would recognize or 

 acknowledge in it a species of his genus Ptycliolepis, so little do its 

 short and thickened proportions resemble the slim, elegant forms 

 of the Sauroid family in general, or correspond with the known 

 species of its own genus ; and yet the inspection of a single scale, 

 or even a fragment of one, would at once reveal to him its true 

 generic afiinity. The fish has retained its natural form without 

 distortion of the body or dislocation of its parts. The pectoral^ 

 ventral, and a portion of the caudal fin are wanting ; with these ex- 

 ceptions, it is in perfect preservation. The length from the nose to 

 the insertion of the tail is 4 j inches, of this measurement the head 

 occupies nearly If inches, more than a third of the entire length 

 In Ptycliolepis Bollensis, the head meastires only a fourth of the 

 total length. The depth of the body at the dorsal fin is l^V iiiches. 

 These proportions . serve to distinguish this from the previously 

 known species; they are, however, associated with other distinctive 

 features to be mentioned in the sequel. The head, as noticed above, 

 is large ; the outline forms a very regular isosceles triangle. The 

 [vilL viii.] 8 I 



