82 FOSSIL FISHES OF THE ENGLISH CHALK. 



fig. 1, el.), best seen in Brit. Mns. no. P. 5685, is sigmoidally bent and tapers at each 

 end. Its upper half expands behind into a nearly smooth, crescent-shaped plate, 

 which is exposed above the pectoral fin, and clearly overlaps a smooth, post- 

 clavicular plate both in the type specimen and in the original of PL XVII, fig. 5 

 (pel.). The scapula, partly exposed in the latter specimen (sc), is relatively small 

 and pierced by an oval foramen. The coracoid, seen in position (cor.), is narrow 

 and deep, produced and tapering below to the clavicular symphysis. The pectoral 

 fin must have been small and delicate, and it is rarely seen. Remains in the 

 original of PL XVII, fig. 1 (pet.) and in B. M. nos. 49083, P. 5418 a, show that it 

 consisted of ten to twelve rays, which are quite feeble compared with those of the 

 other fins. The pelvic bones are so far forwards that they may have been originally 

 in actual contact with the lower end of the clavicles. They are much-expanded 

 laminae (broken in PL XVII, fig. 5, ph.), but their exact shape has not been clearly 

 observed. The pelvic fins are shown by several specimens to be remarkably large, 

 extending, when adpressed to the trunk, to the origin of the anal fin. Each of 

 them consists of seven or eight very stout rays, all articulated and all, except 

 perhaps the foremost, finely divided in their distal half. In the original of 

 PL XVII, fig. 5, the base of the foremost and stoutest ray of the pelvic fin is 

 ornamented with transverse, partly oblique rugae ; while its articulated distal 

 portion is represented only by scattered fragments. The median fins are best 

 shown in PL XVII, fig. 1, but they are always imperfect in the fossils. The 

 dorsal (do.) is remarkably extended and elevated, and is proved to have consisted 

 of :it least 20 rays, probably more. Where the distal parts of the rays are 

 preserved, they are clearly articulated and sometimes divided. The length of some 

 of the hinder rays equals about two-thirds the depth of the trunk at their inser- 

 tion. The anal fin (a.) arises nearer to the caudal than to the pelvic fins, and seems 

 to have had its origin opposite the hinder end of the dorsal fin. It comprises 

 about 12 rays, all articulated and most of them finely divided distally. The caudal 

 fin (PL XVII, fig. 1, c; PL XVIII, fig. 1, c.) is stout and clearly forked. 



The regular and uniform arrangement of the squamation is well shown in 

 many specimens. The number of scales in each transverse series on the flank of 

 the abdominal region is 18 or 19, the lowermost being bent along its median 

 longitudinal axis to enter both the flank and the flattened ventral face. This 

 narrow face is covered by three longitudinal series of scales in addition to the half- 

 scales of each side. All the scales are deeply overlapping, and their exposed area 

 is usually deeper than broad. When unabraded (PL XVIII, figs. 5, 5 a) they are 

 externally ornamented with large flattened tubercles, which give the surface a 

 reticulate appearance, especially conspicuous in the abdominal region; and they 

 are always finely pectinated at their rounded hinder border (fig. 5 a). When 

 abraded, the very fine concentric lines of growth are seen. The overlapped 

 portion of each scale, displaying only these lines of growth, is truncated at the 



