6 



BKITISH FOSSILS. 



vv^ere derived from the Purbeck strata at Hartwell, near Aylesbury. 

 Through the kmdness of Dr. Lee, who has obtained a large number 

 of specimens from the same locality, and who most liberally for- 

 warded them to London for my inspection, I am enabled to com- 

 plete the characters of a fifth species of this genus, which I have 

 named Pleuropholis serratus. The specimens are for the most part 

 so fragmentaiy that I have found it necessary to compile the specific 

 characters from the examination of several individuals. The most 

 perfect specimen (the only one indeed which conveys the form of the 

 fish) is represented in the accompanying Plate, Fig. 5. The head 

 and tail are both imperfect, and the body is a mere impression, the 

 counterpart of which has, unfortunately, not been preserved. This 

 Pleuropholis resembles the other members of the genus in the 

 arrangement of the scales and the disposition of the natatory 

 organs. It difi*ers in its more massive proportions, and in having the 

 posterior edges of the scales serrated. The body is short and deep, 

 compared with the other species resembling in general outline the 

 Pholidophori. The dorsal line is nearly straight, the ventral line 

 rounded. The head as seen in the specimen figured No. 7 is small. 

 The mouth opens upwards, and appears to be edentulous. In this 

 character, and in the position of the orbits and form of the opercular 

 fiap, it is so like the head of a Leptolepis, that apart from other evi- 

 dence it might be plausibly assigned to that genus. The pectoral fins 

 seen in the same specimen are of small size, containing about ten 

 rays. The ventral fins are deficient in all the specimens ; the point of 

 attachment, however, of these organs is seen, in Fig. 5 to have been 

 nearly medial. The dorsal and anal fins, as in the other species of 

 the genus, are opposite to each other, and very similar in form and 

 size. The base of the tail is broad, and the scales do not extend so 

 far on the upper lobe as in Pleuropholis attenuatus and longi- 

 caudus. The dorso-ventral series of scales are about forty in 

 number ; of these the first thirty are composed of large scutes, with 

 a few small lozenge- shaped scales above and below. In the ten 

 posterior rows, the scales are more uniform in size. The most 

 appreciable distinctive character of this species is found in the 

 serrated margin of the scales. This is more or less seen in all the 

 specimens I have examined, but generally in the impression of the 

 scales ; the scales themselves being in so brittle a condition that 

 they are never well preserved. The specimen I have selected to show 

 the dermal characters is figured No, 6. on the plate. Figs. 8 and 9, 

 shoAV the outer surface of the scale and the inner surface of the 

 scale 6, enlarged. 



