Sir P. de M. Grey Egerton on Prognathodus Giintheri. 147 



(which was followed by the formation of the oolitic escarpment) 

 that its present relation to the river-courses has been brought about. 

 The author also referred to the courses followed by the rivers of the 

 more northern part of England, and indicated their relations to the 

 general dip of the strata. 



March 6, 1872.— Prof. Duncan, F.R.S., Yice-President, 

 in the Chair. 



The following communications were read : — 



1. " Prognathodus Giintheri (Egerton), a new Genus of Eossil Fish 

 from the Lias of Lyme Eegis." By Sir P. de M. Grey Egerton, 

 Bart., M.P., E.R.S., E.G.S. 



In this paper the author described a new form of fossil fish 

 having a broad premaxillary plate somewhat resembling the incisor 

 tooth of a gigantic Rodent, a single maxiUary plate like that of 

 CaUorhynclius, and a mandibular dental apparatus closely resembling 

 that of Cochliodiis. Eor this form he proposed the establishment of 

 the new genus Prognathodus, and named the species P. Gimtheri, 

 Iscliyodus Johnsoni, Agassiz, also probably belongs to this genus, as 

 it agrees with P. Giintheri in the characters of the premaxillary 

 teeth. The author was doubtful as to the exact position of this 

 genus, which had a head extended in a horizontal instead of a ver- 

 tical plane, suggesting a resemblance to Zygcena, but covered with 

 hard plates like the head of a sturgeon, and exhibited in the dental 

 apparatus the curious combination indicated above. 



Dr. GtJjS'Ther pointed out the interest attaching to the dentition 

 of this fossil fish as beijig an additional evidence in favour of the 

 connexion between the Ganoid and Chimaeroid forms. The exist- 

 ence of three teeth instead of one on each side of the jaw, as in 

 Ceratodus and others, presented in it a generic character ; but the 

 type was still the same. On one point he slightly differed from the 

 view of the author ; and that was as to the application of the terms 

 maxillary and premaxillary to the teeth. He thought the former 

 belonged rather to the pterygo-palatine arch, and that the teeth in 

 the front of the jaw should be regarded as vomerine. He illustrated 

 this by reference to the jaws and dentition of sharks, Chimaeroids, 

 and certain Ganoids, such as sturgeons. In these the teeth, instead 

 of being connected with the maxillary and premaxillary bones, 

 were, in fact, connected with the pi^erygo-palatine arch. He con- 

 sidered that this furnished additional grounds for including all three 

 forms in one subclass. 



2. ^' On two specimens of Iscliyodus, from the Lias of Lyme 

 Pegis." By Sir P. de M. Grey-Egerton, Bart., M.P., F.P.S., E.G.S. 



In this paper the author noticed a new example of the greatly 

 developed rostrum of a male Chimeeroid, an inch shorter, more 

 slender, and more attenuated at the apex than that of Iscliyodus 

 orthorhinus, Egerton, having a projecting median rib along the upper 

 surface, and the tubercles of the lower part smaller and fewer than 

 in /. orthorhinus. Eor this form the author proposed the name of 



L2 



