L36 FOSSIL FISHES OF THE ENGLISH CHALK. 



Horizon and Localities. — Zone of Bhynchonella cuvieri : Wouldham, Kent 

 (G. E. Dibley Coll.); South Ferriby, Lincolnshire (H. C. Drake Coll.). Probably 

 /.one of Terebratulina gracilis: Mailing, near Lewes, Sussex. Probably also zone 

 of ScJdoenbachia varians : Barrington, Cambridge (Sedgwick Museum). 



Genus THRISSOPATER, Giintlier. 



Thrissopater, A. Giintlier, Figs, and Descript. Brit. Organic Remains, dec. xiii (Mem. Geol. Surv., 



1872), No. 1. 



Generic Characters. — Trunk somewhat laterally compressed; abdomen com- 

 pressed to an edge. Skull as in Pachyrhizodus. Teeth conical and enamelled 

 nearly to the base, where they are fused with the supporting bone ; a single series 

 iu the dentary, premaxilla, and maxilla. Premaxilla without inner horizontal 

 extension ; a single supramaxilla. Vertebras about 50 in number, the centra 

 rarely deeper than long, slightly constricted, smooth or delicately ridged. An 

 enlarged postclavicular scale above the pectoral fin; pelvic fins opposed to the 

 short dorsal ; anal fin relatively small ; caudal fin deeply forked. Scales small or 

 of moderate size, usually ornamented with delicate radiating ridges ; no enlarged 

 or thickened ridge-scales ; lateral line inconspicuous. 



Type Species. — Thrissopater salmoneus (Giintlier, loc. cit., 1872, no. 1, pi. i) 

 from the Gault of Folkestone, Kent. 



Remarks. — This genus appears to differ only very slightly from Pachyrhizodus. 

 The dentition is more feeble, without inner teeth on the premaxilla. The trunk 

 seems to have been less rotund. 



A skull showing a gular plate, Avhich I once assigned to Thrissopater (Catal. 

 Foss. Fishes B. M., pt. iv, p. 33), now proves to belong to Osmeroides. The gular 

 plate, therefore, still remains unknown. 



1. Thrissopater megalops, A S. Woodward. Plate XXVIII, fig. 5. 



I'.Mil. Thrissopater (?) megalops, A. S. Woodward, Catal. Foss. Fishes B. M., pt.iv, p. 35, pi. vii, fig. 4 



Type. — Imperfect head probably from zone of Holaster subglohosvs ; British 

 Museum. 



Specific Characters. — Posterior suborbital plates relatively narrow, their extent 

 not exceeding one quarter the length of the skull ; orbit very large, its width con- 

 siderably greater than one third the length of the skull ; teeth of premaxilla 

 relatively long and slender, larger than those both of the maxilla and dentary. 

 Opercular apparatus relatively narrow, its width not exceeding one third the 

 length of the skull. Radiating lines on anterior scales few and indistinct. 



