2 



BRITISH FOSSILS. 



constituted. The pectoral fins are composed of numerous broad 

 flattened rays. They have frequent transverse joints, and are re- 

 markable for having their surface invested with a corrugated layer 

 of ganoine, corresponding in character with that covering the head 

 bones and scales. This character is common to all the fins. The 

 only similar instance I am acquainted with occurs in. the genus 

 Platysomus. The first pectoral ray is fringed with scales on its 

 anterior border. The position of the ventral fins is seen about 

 midway between the pectoral and anal fins ; the fins themselves 

 are defective. The space between the pectorals and the anal is so 

 confined that the ventral fins were probably of small dimensions. 

 The anal fin is very large, and the rays composing it unusually 

 long. The first ray h.is fulcral scales and a fringed margin ; the 

 subsequent rays are flattened, expanded, and transversely jointed 

 at short intervals ; in number they cannot have been fewer than 

 thirty. A few rays of each lobe of the tail are preserved ; the 

 multiplication of the transverse articulations is the most striking 

 peculiarity they present. A single broad scale occurs at the base 

 of the lower caudal lobe, but beyond this no fulcral scales seem 

 to have existed in this region. The scales are unlike any I have 

 elsewhere met with ; they are rhomboidal, of medium size, and 

 extremely solid. The exposed surface is covered with coarse rugae, 

 arranged, not, as is commonly the case, in the longitudinal direction, 

 from the anterior to the posterior margin of the scales, but trans- 

 versely. The free edges of the scales are armed with strong spurs. 

 On the under surface the scales are smooth, and destitute of the 

 midrib so common in the generality of the Sauroid genera. The 

 substance of the scales is so thick that the strong articulating pro- 

 cesses of the upper margins are formed out of the uniform thickness 

 of the scales themselves, the extra material provided by the midrib 

 not being requisite. I am not without hopes that the publicity 

 given to what is already known respecting this genus may be the 

 means of bringing to light other specimens, to complete the anato- 

 mical details of this most interesting form. 

 Locality. — Lias of Lyme Regis. 



Explanation of Plate. 



rig. 1. Centrolepis asper, size of nature. 



rig. 2. Scales, magnified. 



Fig. 3. Caudal scale, magnified. 



P. DE M. Grey Egerton. 



February 1857. 



