189 



pscudolmrengus (alewifc) ; but, in that species it articulates posteriorly with a 

 process of the ethmoid, instead of the prefontal. In the blucfish (Poiiiatomus 

 saltatrix) there is a nearer approach ; here, the malleolus articulates with tlic 

 prefontal and maxillary, but with the latter only by a squamosal joint. The 

 same species betrays a resemblance to. this family ia the insertion of the 

 teeth by roots in alveoli, but the roots are much shorter in the living genus. 

 They are also accompanied by a series of foramina on the inner side of the 

 dcntary, as in Saurocephalus. 



Six genera are enumerated below as belonging to this fi\mily, of which 

 one, Erisichthc, Cope, is placed in it provisionally : 



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 Porthcus. 



Teeth of equal lengths - Ichthyodcclcs. 



aa. Teeth compressed, knife-liUe : 



Teeth of unequal lengths; some of the anterior ■ 



greatly develojied Erisichthc. 



Teeth equal. Daptinus. 



II. Dentary bones pierced by foramina l)clow the alveolar 

 border : 



Teeth with subcylindric crowns Saurodon. 



Teeth witli short, compressed crowns Saurocephalus. 



There are some other forms to be referred to this family, whose cliarac- 

 ters are not yet fully determined. Thus, Hypsocbn, Agass., from the European 

 chalk, is related to the two genera first named above, but, as left by its 

 author in the " Poissons fassiles," 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 referred. Both are physostomous fishes, and not related 

 to the Sphyranidce, wliere authors have generally placed them. Retaining 

 the name Hxjpsodon for the genus with equal mandibular teeth, its relations 

 to Ichthrjodecles remain lo l)e determined liy liutlun- study of the H. Icvesiensis. 



