2 



BRITISH FOSSILS. 



the tail. The bones of the head are marked with irregular, pro- 

 jecting lines at distant intervals, interspered with small isolated 

 tubercles. The opercular bones are similarly ornamented, but 

 the intervals between the lines are rather larger. A few scales im- 

 mediately behind the scapular arch, on the central part of the body, 

 are of large size. These are traversed by five or six longitudinal 

 sinuous furrows, and terminate with a serrated margin. They are 

 succeeded by scales more elongated, and having fewer and more 

 regular furrows, and these on the dorsal, ventral, and anal regions 

 give place to the narrow elongated scales (fig. 5.) peculiar to this 

 genus. All the scales have their bases, — or those parts overlapped 

 by the antecedent scales, — marked by parallel, transverse plicae, show- 

 ing the periods of growth. In this character they resemble the 

 scales of Pholidophorus crenulatus, and some Palceonisci. The pec- 

 toral fin is broad at the base, and pointed at the termination. It is 

 composed of about 30 rays. The transverse articulations of the rays 

 are frequent near the base, but very distant in the other portions of 

 the fin. The dorsal, ventral, and anal fins are wanting. The tail 

 is small and elegantly forked. The articulations of the rays are 

 more numerous in the lower than in the upper lobe, but the intervals 

 between them become greater as they recede from the base. In 

 these respects this organ has considerable resemblance to the caudal 

 fin of Pholidophorus. The endo-skeleton in this genus was pro- 

 bably entirely cartilaginous, since I have been unable to discover in 

 any specimen the least trace or impression of the spinal column or 

 its appurtenances. 



Affinities. — The genus Ptycholepis is considered by Agassiz to be 

 most nearly allied to Eugnathus. This opinion is founded upon the 

 characters of the scales and teeth. The latter I have not been able 

 to detect in my specimens. In other respects it has considerable 

 resemblance to the Pholidophori, and especially to some of the 

 narrow-scaled species of that genus, which I have proposed to remove 

 to the new genus Histionotus. These features, together with the 

 absence of a bony endo-skeleton, which is of considerable solidity in 

 Eugnathus, lead me to infer that the Ptycholepides were altogether 

 more feeble and less predatory than the Sauroid genera, with which 

 they are allied. 



Locality. — The specimen above described was found in the lias 

 quarries at Barrow-on-Soar, and is the only example of this species 

 I have met with. The two halves are in the possession of Lord 

 Enniskillen and myself. 



