SUPPLEMENT. 245 



middle raised portion of a dental crown, and was obtained from an undetermined 

 horizon near Winchester. It rises to an obtusely pointed apex, from which two 

 antero-posterior, and two lateral ridges radiate at right angles to each other. 

 Small irregular branches from these ridges, with other intercalated branching ridges, 

 fill the sectors between them. All these ridges end below in vermiculations, which 

 gradually pass into the fine granulation of the marginal area, of which only a 

 fragment is seen in the fossil. So far as preserved, therefore, the specimen 

 cannot be distinguished from a tooth of P. morUmi, but its specific determination 

 must remain provisional until complete teeth of the same form are discovered. 



P. mortoni has been regarded as the type of a sub-genus, Hemvptychodus, by 

 Jaekel 1 ; but the discovery of the nearly complete dentition of this species in the 

 Chalk of Kansas, 2 and the frequent tendency to radiation of the tooth-ridges in 

 P. decurrens, suggest that such complication of nomenclature is hardly necessary. 



SUPPLEMENT. 



Berycopsis elegans, Dixon (p. 5) Plate LIII, fig. 1. 



The new specimen shown of tw T o thirds the natural size in PI. LIII, fig. 1, is 

 interesting as exhibiting the shape and proportions of the caudal region. It was 

 obtained by Mr. W. E. Balston from the zone of Hulaster subglobosiis at Hailing, 

 Kent, and was presented by him to the British Museum. The head is displaced 

 forwards and upwards, while the greater part of the jaws and the opercular bones 

 are wanting. The anterior region of the trunk is somewhat depressed by 

 crushing, as shown by the displacement of the scales; and its ventral portion 

 is partly destroyed. The tail, however, seems to exhibit very little distortion. 

 It is thus clear that the caudal region between the dorsal and anal fins is less 

 tapering than it is represented to be in the restored figure of the species on 

 p. 7 (Text-fig. 2) ; that it is, in fact, shaped as in Platj/cormus germanus, from the 

 Senonian of Westphalia. The narrow caudal pedicle is also longer than it was 

 supposed to be. The well-preserved equalisation extends over the bases of the 

 dorsal and anal fins, as already observed in other specimens; and it is also seen to 

 pass gradually into small scales which cover the basal part of the caudal fin. The 

 caudal fin-rays are much broken and their distal portions are destroyed. Only 

 parts of the anterior spines and the undivided proximal ends of the other rays of 

 the dorsal and anal fins are preserved, so that the shape of these fins still remains 

 unknown. 



1 O. Jaekel, Die eociineu Selachier vom Monte Bolca (1894), p. 137. 



2 S. W. Willistou, " Cretaceous Fishes," Univ. Geol. Surv. Kansas, vol. vi (1900), p. 238, pis. xxv- 

 xxvii. 



