BRITISH FOSSILS. 



5 



lobe of the caudal fin is covered by an oblique prolongation of the 

 scales of the tail. The upper margin of the fin is roofed with 

 a series of elongated, imbricated scales, similar to those seen in the 

 genus Ophiopsis, and common to most of the heterocerque fishes. 

 The rays composing the fin are from twenty to thirty in number, 

 and are long and powerful for the size of the fish. The pedicle of 

 the tail is narrow, allowing great latitude of motion to the pro- 

 pelling organ. The general arrangement of the large scutiform 

 scales investing the flanks of the fish corresponds with that described 

 in the foregoing memoir ; and is, in fact, a generic rather than a 

 specific character. The scales on the back and belly are small and 

 lozenge-shaped ; these are connected, above and below, with the prin- 

 cipal longitudinal series of high and narrow scutiform scales covering 

 the parietes of the thorax and abdomen. Beyond the hinder part 

 of the dorsal fin, the smaller scales encroach more and more on the 

 principal series, and the latter diminish in altitude, until, in the 

 proximity of the tail, all the scales are nearly uniform in size. The 

 outlines of the scales in the principal series are waved in double 

 curvatures, representing a series of parallel sigm^oid lines of very 

 graceful appearance, the curves becoming gradually less, until, in 

 the caudal region, the scales are nearly rectilinear. All the scales 

 are invested, on the outer surface, with a thick and shining coat 

 of ganoine, without sculpture, and unbroken at the posterior margin. 

 The under surfaces have broad, slightly elevated bands, occupying 

 the median area of each scale (fig. 9). The connexion with the 

 lozenge-shaped scales of the back and belly is provided for by 

 a small process at the upper and a slight depression at the lower 

 extremities of these bands. 



Locality. — The specimen belonging to Mr. Lister is from near 

 the bottom of the Downs vein of the Purbeck section, which, as 

 I am informed by Mr. Austen, corresponds with the bed No. 69 in 

 his tabular arrangement. Mr. Brodie's specimen is from the same 

 region of the section, and Mr. Austen's is from a thin shale sub- 

 ordinate to bed 48 of his economic table, which corresponds with 

 No. 69 of the Durdlestone Bay section. 



PLEUROPHOLIS SERRATUS. Sp. Nov. 



Plate VII. Fig. 5—9. 



I have recently ascertained that the specimens in the i\Iuseum of 

 Practical Geology indicating another species of Pleuropholis, to 

 which I alluded in the description of Pleuropholis longicaudus, 



