100 WEALDEN AND PURBECK FOSSIL FISHES. 



large peg-and-socket articulation, and their inner face is strengthened by a wide 

 vertical ridge. In the caudal region this articulation gradually disappears. 

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



Genus BELONOSTOMUS, Agassi/. 



Belonostomus, L. Agassiz, Nenes Jahrb. fur Min., etc., 1834, p. 388. 



Ophirhachis, 0. G. Costa, Ittiol. Foss. Ital., 1856, p. 13. 



Diphyodus, L. M. Lambe, Contrib. Canadian Palseont., vol. iii, pt. ii, 1902, p. 30. 



Generic Characters. — As Aspidorhynchus, but mandible almost or quite as long 

 as the rostrum, and all the scales of the lateral line deeper than those immediately 

 beneath. 



Type Species. — Belonostomus sphyrseuoides (L. Agassiz, Poiss. Foss., vol. ii, 

 pt. ii, 1844, pp. 140, 2 ( .»7, pi. xlviia, fig. 5), from the Lithographic Stone (Lower 

 Ivimmeridgian) of Bavaria. 



1. Belonostomus hooleyi, sp. nov. Plate XXI, figs. 1—3. 



Type. — Imperfect principal scale of flank; collection of Reginald W. Hooley, Esq. 



Specific Characters. — Principal deepened scale of flank smooth, sometimes with 

 traces of large elongated tubercles near the anterior border, and marked by one 

 conspicuous vertical groove ; the posterior border very coarsely and irregularly 

 crenulated and pectinated. Dorsal scales ornamented with a few large, low, and 

 irregular short longitudinal ridges. Roof of skull with similar coarse ornament. 



Description, of Specimens. — The type scale (PI. XXI, fig. 1) is incomplete below, 

 and most of its smooth outer surface has been flaked away ; but it is well preserved 

 at the forwardly bent upper end, where the slightly tumid anterior half is clearly 

 separated by a sharp vertical line from the flatter posterior half. At the upper 

 end the posterior border seems to be entire, but below this it is very coarsely and 

 irregularly crenulated, each prominence being bluntly pointed and forming a slight 

 horizontal ridge. 



The same form of flank-scale is distinguishable in the fragmentary pyritised 

 remains of a fish in the Mantell Collection, which also includes the hinder half of 

 a cranium and traces of vertebrae. The flattened roof of the skull must have been 

 very coarsely ornamented with irregular rounded ridges and low elongated tubercles. 

 All the otic bones and apparently the alisphenoid are well ossified ; and an anterior 

 vertebral centrum, evidently fused with the basioccipital, is more extensively ossified 

 than the ordinary vertebral centra of Aspidorhynchus. Another centrum among the 

 scales shows that it is pierced in the middle for a persistent strand of the noto- 

 chord. The rhombic dorsal scales (PI. XXI, fig. 2) are as coarsely ornamented 



