19G FOSSIL FISHES OF THE ENGLISH CHALK. 



Type. — Jaws, vertebrse, etc, in natural association, from zone of HoJaster 

 subglohosiis ; British Museum. 



Specijic Characters. — Anterior teeth with a single pair of small, stout lateral 

 denticles ; outer face marked with prominent vertical striiie in its basal half. 



Description of Specimen. — This species is still known only by the type specimen 

 (PI. XLII, fig. 7), Avhich displays the jaws from below, with part of the vertebral 

 column and the pectoral arcli. The cartilage is superficially calcified in small 

 polygonal tesserae with fringed margins, which were mistaken by Agassiz for 

 shagreen (lac. cit., fig. 4). The pterygoquadrate {ptq.), or cartilage of the upper 

 jaw, is nnicli more slender than the mandible, and bears on its outer face, Avithin 

 the hinder half, a small prominence {x.), from which seems to haA^e been suspended 

 a slender labial cartilage (/.). Each mandibular ramus {uul.) is very deep behind, 

 impressed by a large muscular fossa on the hinder half of its outer face ; and the 

 mandibular symphysis is rather Avide. Traces of the hyoid (////.) and other 

 cartilages are seen behind the jaAVS, but the greater part of the branchial apparatus 

 is destroyed. The vertebral centra in front of the pectoral arch {p)ct.) are not Avell 

 shoAvn, but just behind it they are short and deep and very clearly strengthened 

 by radiating calcified plates. The pectoral arch (fig. 11) is a narroAv transverse 

 band of cartilage, turned shar})ly upwards at each end at the articulation for the 

 fin, and its ascending portion tapering rapidly upwards to a point. 



In the fossil, teeth are slioAvn only near the symphysis. Four display the outer 

 face (figs. 8, 9), Avhicli is consj^icuously striated except near the apex. The stout 

 lateral denticles are distinct in three of these teeth, Avhile they are scarcely marked 

 in the fourth. When viewed from beloAV (fig. 10) the flattened root exhibits 

 a large oval foramen, and the middle part of the anterior face of the crown is seen 

 to be produced dowuAvards. 



Horizon and Localltij. — Zone of ITolastev snbgJobosiis : liurham, Kent. 



FamUij Lamnid^. 



The Cretaceous sharks of the family Lamnidae are best known l)y associated 

 sets of teeth and vertebree from the Chalk of Kansas, U.S.A., and by some well- 

 preserved small fishes {Scapanorliynclms) from the fissile limestone of Mount 

 Lebanon. Nearly all the teeth and vertebrae in the English Chalk are found 

 scattered and isolated. The teeth are always solid, without central cavity. 



Goiiis CORAX, Agassiz. 



Corax, L. Agassiz, Poiss. Foss., vol. iii, 1843, p. 224. 



Pseudocorax, F. Prieiu, Bull. Soc. Greol. France [3], vol. xxv, 1897, p. 47. 



Generic Characters. — Teeth compressed, more or less triangular in shape, 



