1 \2 



FOSSIL FISHES OF THE ENGLISH CHALK. 



in the same specimen probably represent remote dorsal and anal (a.) fins 

 opposed to each other. The caudal fin (c.) consists of very stout, closely articulated, 

 and finely divided rays ; and their remains shown in fig. 13 suggest that it was not 

 forked. 



Variations. — In some of the jaws usually referred to Tomognathus mordiw, the 

 teeth are comparatively slender and exhibit scarcely any traces of the vertical 

 flutings. These are of the form named T. leiodus by Dixon, but intermediate 

 specimens appear to prevent their reference to a distinct species. 



Horizon and Localities. — Zone of Holaster subglobosus : neighbourhood of Bnrham 

 and Dover, Kent ; Washington, Southeram (near Lewes), and Amberley (near 

 Arundel), Sussex ; Dorking, Surrey. The same or an allied species in the Chalk 

 Marl (zone of Schloenbachia variant) : Dover. 



Sub-order ^ETHEOSPONDYLI. 



Family Aspjdoehynchid.e. 



This family is known only by two genera, Aspidorhynchus and Belonostomus. 

 All the species of Aspidorhynchus (Text-fig. 41) are Jurassic, but a few of the larger 

 species of Belonostomus occur in Cretaceous formations in Europe, Mexico, Brazil, 

 and Queensland. 



Genus BELONOSTOMUS, Agassiz. 



Belonostomus, L. Agassiz, Neues Jalirb., 1834, p. 388. 

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



Generic Characters. — This genus differs from Aspidorhynchus (Text-fig. 41) in 



Pig. 41. Aspidorhynchus acutirostris (Blainville) ; restoration, about one seventh nat. size. — Upper 

 Jurassic (Lithographic Stone) ; Bavaria. From Catal. Foss. Fishes B. M., pt. iii, 1895. 



having the mandible almost, if not quite, as long as the rostrum, the postorbital 

 cheek-plates in direct contact with the preoperculum, and all the scales of the 

 lateral line deeper than those immediately beneath. 



Type Species. — Belonostomus sphyrxnoides (Agassiz, Poiss. Foss., vol. ii, pt. ii, 

 L8 I I, pp. 140, 207, 1)1. xlviia, fig. 5), from the Upper Jurassic Lithographic Stone 

 of Bavaria. 



