HYPSODON ETC. FROM BRITISH CRETACEOUS STRATA. 509 



and depressed, that of Poriheus is narrow and compressed ; the 

 vertebrae also are shorter than in Portheus, and have not the large 

 lateral pits or depressions. 



Portheus, Cope. 



This genus was established by Prof. Cope to receive certain large 

 fossil fishes from the Cretaceous formations of the Western Terri- 

 tories. The genus is fully described ; and the more important cha- 

 racters by which it is separated from other genera of the Saurodon- 

 tidse are thus given (loc. cit. p. 190): — " Teeth subcylindric, without 

 serrate or cutting edges, occupying the premaxillary, maxillary, 

 and dentary bones ; sizes irregular ; the premaxillary, median 

 maxillary, and anterior dentary teeth much enlarged. No foramina 

 on inner face x>f jaws. Teeth on the premaxillary reduced in 

 number. Opercular and preopercular bones very thin. Cranial 

 bones not sculptured." 



The only examples of this genus at present known in Britain are 

 also from Cretaceous formations ; and by far the most perfect speci- 

 men with which I am acquainted is the one from the Gault of Folke- 

 stone described below as Portheus gaultinus, and preserved in the 

 Museum of Practical Geology. There are numerous fragments of jaws 

 belonging to this genus in several provincial Museums and private 

 collections ; but their affinity with Portheus appears not to have been 

 recognized hitherto. 



Prof. Cope's synopsis of distinctive specific characters will help to 

 make more clear the descriptions of new species in the following 

 pages. 



Synopsis of Species. 



a. Two premaxillary teeth : 



Maxillary arch thin, deep, with narrow anterior con- 

 dyle ; large maxillary teeth five ; third mandibular 

 tooth large, behind a cross groove P. molossus. 



Maxillary large teeth three; third mandibular small, 



w ithout cross groove in front of it P. thaumus. 



aa. Three to five premaxillary teeth : 



Maxillary arch stout, deep, with heavy anterior condyle ; 



larger teeth five P. lestrio. 



Maxillary arch thick and shallow ; larger teeth five P. Mudgei. 



aaa. Premaxillary teeth unknown : 



Maxillary bone deeply concave; small P.arcuatus, 



As the representatives of this genus in England are chiefly known 

 to us by fragments of upper and lower jaws, it is particularly con- 

 venient to have this synopsis, which is founded upon the characters 

 of the teeth and jaws. Prof. Cope, having had better and more 

 numerous specimens than we possess, has selected these as pro- 

 minent features, the characters here pointed out being accompanied 

 by other differences in various parts of the skeleton. 



