NEORHOMBOLEPIS. 87 



Description of Specimens. — This species is still known only by isolated dentary 

 bones and maxillse, which are not uncommon in the Middle Purbeck Beds of 

 Swanage. As they are smaller than some of the corresponding' bones of G. pur- 

 beckensis, they might at first be regarded as representing the young of the latter 

 species ; but if dentaries of nearly the same size be compared (as in PI. XIX, figs. 

 2, 4), the more slender proportions of G. tenuidens are evident. All the teeth, 

 when well preserved, exhibit the usual little triangular apex of translucent gano- 

 dentine. The characteristic maxilla shown in inner view in PI. XIX, fig. 8, is 

 nearly complete, displaying the shape of the hinder slight expansion and the 

 depressed anterior half of the bone. 



Horizon and Locality. — Middle Purbeck Beds : Swanage, Dorset. 



Genus NEORHOMBOLEPIS, A. S. Woodward. 

 Neorhombolepis, A. S. "Woodward, Proc. G-eol. Assoc, vol. x, 1888, p. 304. 



Generic Characters. — Trunk elongate-fusiform, more or less laterally compressed, 

 and head relatively large. External head-bones and the opercular bones stout, 

 more or less ornamented with tubercles and rugve of ganoine, but no prominent 

 bosses or outgrowths. Maxilla with a straight tooth-bearing border and a long 

 supramaxilla; teeth conical, in regular series, large and hollow on the margin of 

 the jaw, not in sockets ; a patch of minute teeth on the parasphenoid. Sub- 

 operculum at least half as large as the operculum, which is quadrangular but 

 truncated at the postero-superior angle. Vertebral centra either ring-shaped or 

 completely ossified. Fulcra well-developed on the pectoral fins, probably on the 

 other fins. Scales rhombic and thick, with a wide overlapped margin not pro- 

 duced at the angles, and the peg-and-socket articulation feeble or wanting ; super- 

 ficial ganoine nearly smooth; few principal flank-scales as deep as broad, the 

 majority broader than deep, and those of numerous ventral series at least twice as 

 broad as deep, sometimes subdivided. 



Type Species. — Neorhombolepis excelsus (A. S. Woodward, Proc. Geol. Assoc, 

 vol. x, 1888, p. 304, pi. i, fig. 1 ; also Foss. Fishes of English Chalk — Pal. Soc, 

 1909 — p. 158, pi. xxxiv, fig. 1) from the English Lower Chalk. 



Remarks. — A detailed study of the type specimen of the Weald en species 

 described below, modifies the original definition of Neorhombolepis by making- 

 known the fulcra on the pectoral fins. 



1. Neorhombolepis valdensis, A. S. Woodward. Plate XVIII. 



1895. Neorhombolepis valdensis, A. S. Woodward, Catal. Foss. Fishes B.M., pt, iii, p. 356, pi. viii, 

 fig. 5. 



