HYPSODON ETC. FROST BRITISH CRETACEOUS STRATA. 507 



Synopsis of Genera. 



I. Jaws without foramina on the inner face below the alveolar 

 margin. 



a. Teeth cylindric. 



Teeth of unequal lengths ; some of them greatly 



developed Portheus. 



Teeth of equal lengths Ichthyodectes. 



aa. Teeth compressed, knife-like. 



Teeth of unequal lengths; some of the anterior 



greatly developed Erisichthc. 



Teeth equal Daptin us. 



II. Dentary bones pierced by foramina below the alveolar 

 border. 



Teeth with subcylindric crowns Saurodon. 



Teeth with short, compressed crowns Sauroccphalus. 



Immediately after this synopsis Prof. Cope says : — " There are 

 some other forms to be referred to this family, whose characters are 

 not yet fully determined. Thus Hypsodon, Agass., from the Euro- 

 pean Chalk, is related to the two genera first named above, but, as 

 left by its author in the ' Poissons Fossiles,' includes apparently two 

 generic forms. The first figured and described has the mandibular 

 teeth of equal length. In the second, they are unequal, as in 

 Portheus, to which genus this specimen ought, perhaps, to be re- 

 ferred. * * * * Retaining the name Hypsodon for the genus with 

 equal mandibular teeth, its relations to Ichthyodectes remain to be 

 determined by further study of H. levesiensis. The view of the 

 superior walls of the cranium given by Professor Agassiz presents 

 characters quite distinct from what I have observed in Portheus. 

 A species of Ichthyodectes from the chalk of Sussex, England, is 

 figured, but not described, by Dixon in the ' Geology of Sussex.' " 



From this it is seen that Prof. Cope fully recognized the difference 

 existing between the various specimens referred to H. leivesiensis by 

 Agassiz. A comparison of the figures given by Prof. Agassiz of 

 Dr. Mantell's specimen (pi. 25 b. fig. 1) with Prof. Cope's figures 

 (loc. cit. pis. 39, 41, and 42. fig. 1) will show, I think, conclusively 

 the close affinity between them. The peculiar form of the maxilla 

 and proemaxilla, and the large teeth implanted in the latter, corre- 

 spond so closely in the two, that at first sight they might be thought 

 to belong to the same species. 



Having, in the light of Prof. Cope's memoir, carefully examined 

 Agassiz's type specimens, and compared them with the fish-remains 

 described in the following pages, I am convinced of the necessity of 

 dividing Hypsodon lewesiensis as suggested by Prof. Cope ; and it 

 is proposed to retain this name for the specimens first described by 

 Agassiz, and upon which the species and genus are really founded 

 (Poiss. Eoss. vol. v. pi. 25 a. figs. 1, 2, and 4), and to remove Dr. 

 Mantell's specimens and certain others (Poiss. Foss. pi. 25 a. fig. 3, 

 and 25 6. figs. 1 a, 1 6, 2. and 3) to the genus Portheus of Cope. 



