1893.] OSTEOLOGY OF LEPID0TU8 AXD DAPEDIUa. 563 



articular bone, and to its outer face there is apposed a large plate, 

 probably to be interpreted as anr/uJar (Plate XLIX. fig. 1 d, ag.). 

 The coronoid region of the mandible is very deep, and the summit 

 of the elevation is completed by a very small surawjular bone, shown 

 in a Wealden specimen of L. mantelU (Brit. Mus. no. P. 6342). 

 The dentary bone ('/.), very deep in the coronoid region, becomes 

 much narrower in its tooth-bearing portion ; and its anterior half 

 curves rapidly inwards to meet its fellow of the opposite side in a 

 somewhat deepened symphysis. To the inner side of the dentary 

 bone the robust sjihnial is articulated by a roughened face, and it 

 also enters the mandibular symphysis ; whereas the dentary exhibits 

 only one regular series of teeth, this element has several irregular 

 series of a more tritoral character. 



The ceratohi/al (Plate XLIX. fig. 1 e) exhibits its ordinary 

 hourglass-shaped form, and is deepest behind. The hiipohyah 

 are a pair of verj' small triangular bones (seen in Brit. Mus. 

 no. P. 6341 ) ; and no evidence of an ossified glossohyal has hitherto 

 been observed. 



The opercular apparatus is complete, and there is a good series 

 of branchiostegal rays, the uppermost very broad ; but no indica- 

 tions of a gular plate have yet been discovered in Lepidotua. The 

 last-named fact is all the more remarkable, since in closely allied 

 genera (e. g., Dapedius) the gular plate is relatively large and 

 robust. The preopereulum (Plate L. fig. \,p.op.) is a long narrow 

 bone, exposed throughout its length and much bent forwards below. 

 The opereulum {op.) exhibits a sharp elevation on its inner face for 

 articulation with the hyomandibular process ; its upper border is 

 overlapped by the supratemporal plates, and its lower border 

 deeply overlaps the suhopercidmn. The latter element (s.op.) is 

 almost sickle-shaped, with a very large upwardly-directed process 

 at its antero-superior angle, and abruptly truncated in front for 

 union with the large elongate-triangular interoperculum {i.op.) 



The siipratemporcd plates vary much in arrangement in different 

 species of Lepidotus, but they always overlap both the cranial roof- 

 hones and the most anterior dorsal scales. In L. latifrons (Plate 

 XLIX. fig. 1, St.) there is one not quite symmetrical pair of outer 

 plates, occupying the space between the operculum, squamosal, 

 and parietal on each side; and there are three symmetrically 

 arranged plates no larger than ordinary scales apposed to the 

 hinder margin of the parietals. In L. mantelU the supratemporals 

 are in three pairs, the two outer ones corresponding to the single 

 outer pair in L. latifrons. In L. elvensis, as already described by 

 Quenstedt, the supratemporal series consists of a single pair of 

 large plates, as in Amia. 



II. Ox THE CEASitr>i or Dapedius. 



The Liassic genus Dapedius is so closely related to Lepidotus, 

 that it is interesting to compare the characters of the skull in these 

 two fishes. So far as the external bones are concerned, the restora- 



