1872.] EGEKTON PEOGXATHODUS GtJNTHERI, 233 



1. On PiiOGNATnoDTjs Gii^TTHEEi, Egeiton, a new Genxjs of Fossil 

 Fisn from the Lias of Lyme Eegis. By Sir Philip de M. Geey 

 Egeeioi^, Bart., M.P., F.ll.S., P.G.S. 



[Plate VIII.] 



RepPvEsei^tatives of the ChimDcroid family have hitherto heen of 

 very rare occurrence in the Lias. Li 1847, when I communicated 

 a paper to the Geological Society " On the jSTomenclature of the 

 Possil Chimeeroid Pishes," only one specimen was known, Ischi/ochis 

 Johnsoni, described by Professor Agassiz in the third volume of the 

 ' Poissous Fossiles,' p. 344, and figured on pi. 40c. fig. 22. Although 

 included in the tabular arrangement appended to that paper, I never- 

 theless entertained much doubt as to the real position of this species ; 

 it differed so much from the other members of the famUy in the 

 characters of the premaxillary teeth. 



In the Chimseroid genera, both recent and extinct, these are sub- 

 triangular, composed of parallel columns of coarse dentinal matter 

 arising from a basal pulp-cavity and lodged longitudinally in cavities 

 of a plate of softer material, so that the unequal wear of the two sub- 

 stances serves to maintain notched cutting-edges at the extremities. 

 These multiple denticles are coated externally and internally with 

 a superficial layer of a harder material resembling ganoine. The pre- 

 maxillary tooth of the Liassic specimen differs remarkably in these 

 particulars. Although imperfect, it measures one inch and a half 

 in length, and has a uniform breadth of half an inch. So far from 

 being subtriangular, it resembles somewhat the incisor tooth of a 

 gigantic Rodent, except that the inner facies is concave, and conse- 

 quently the transverse section is crescentic. The profile of the tooth 

 describes a gentle curve from the base to the extremity. The inte- 

 rior is composed of a homogeneous tissue of coarse tubular dentine, 

 enveloped all round with a casing of harder material. The wearing 

 away of these substances produces a sharp chisel-shaped edge without 

 notches or serrations. The maxillary plate is also unlike that of any 

 of the fossil Chimseroids, having the triturating area composed of one 

 broad convex layer of dentine, instead of three molar surfaces as in 

 Edapliodon and Ohimcera, or four, as in Iscliyodus. In this respect 

 it has more resemblance to CaUorhynchus. The mandibular plates 

 exhibit the same peculiarity of having the triturating surfaces con- 

 tinuous instead of being interrupted by bony septa (as is the case 

 in the other members of this family). All these teeth have those 

 exposed surfaces which are not subject to attrition in mastication 

 invested with a thin layer of ganoine, corresponding, in this respect, 

 with the typical Chima^roids. 



After waiting patiently more than twenty years for further mate- 

 rials to elucidate this aberrant form, a specimen has come into my 

 hands, through the good offices of Lord Enniskillen and Dr. Giin- 

 ther, which throws some light upon this subject. The specimen 

 has been for some time in the possession of a man named More, at 

 Lyme Eegis, who, fancying he had found a fossil Bat, set so extra- 

 vagant a price upon it that he had the satisfaction of retaining it in 

 VOL. xxviii. — pabt I. s 



