ATHRODON. 47 



This articulation, however, is comparatively feeble, while the inner vertical ridge 

 connected with it is low and irregularly widened (fig. 8). On the middle of the 

 flank, the upper process of the wide overlapped margin of each scale is longer and 

 more slender than the lower process (figs. 7, 8). In the dorsal, ventral, and 

 caudal scales, the inner face is tumid, and there is no peg-and-socket articulation 

 (PI. XI, figs. 10 a — 13 a). Some of the scales in the dorsal part of the abdominal 

 region are nearly square, and their straight overlapped border is prolonged 

 upwards into a strong process (PI. XI, figs. 9, 10). In the more elongated scales 

 of the ventral part of the abdominal region the overlapped margin is forked as in 

 the scales of the flank, with the upper process much longer than the lower process 

 and often inclined upwards (PI. XI, figs. 11, 12). In the caudal region (PI. XI, 

 fig. 13), the anterior overlapped margin is comparatively narrow, and the inner 

 face (fig. 13 a) remarkably tumid. An isolated scale of the lateral line in the caudal 

 region (figs. 14, }-ia) shows especially well the two orifices on the outer face for 

 the slime-canal and its posterior exit on the inner face. 



Affinities. — Lepidotus manfelH appears to be most closely related to Lepichtus 

 Isevis, Agassiz, as interpreted by F. Priem, who describes the greater part of a fish 

 from the Lower Kimmeridgian of Cerin (A in), France, in Annales de Paleontologie, 

 vol. iii (1908), p. 2, pi. i. 



Horizon (uid Localities. — Weal den : Sussex and (?) Isle of Wight. Upper 

 Purbeck Beds : Sussex. 



Undetermined species of Lepidottis about as large as L. manteJli are known by 

 fragments from the Middle Purbeck Beds of Swanage, Dorset. Part of a trunk 

 about 25 cm. in maximum depth in the Dorset County Museum, has smooth scales 

 without serrations. The opercular and anterior region of an equally large fish in 

 the British Museum exhibits a coarse irregular serration of the smooth scales. 



One or more undetermined dwarf species of Lepidotus also occur in the Purbeck 

 Beds of the Vale of Wardour, Wiltshire. 



Family Pygnodontid^.. 

 Genus ATHRODON, Sauvage. 



Athrodon, H. E. Sauvage, Bull. Soc. Ge'ol. France [3], vol. viii, 1880, p. 530. 



Generic Gharncters. — Splenial bone unusually stout, with a deep symphysial 

 facette ; its oral face covered with rounded teeth, which are arranged in more or 

 less irregular longitudinal series, the one principal series generally not well 

 differentiated from the others. 



