210 



tcetli ; Viiit the extent to wliich it enters into the superior arcade of the 

 nioutli varies. It is shortest in Enipo, and longest in Pachyrhizodtts. The 

 pnMnaxillary is greally extended in E/njm, and shortest in Tethcoflus and 

 Sfraloflus. The teeth differ from those of th(! Smirodojifirla- in their nuxh; 

 of attachment; instead of being inserted by long roots into (Icc]) alveoli, they 

 are anchylosed by the base to the alvcobar border of tlie jaw, vvhieli may 

 sometimes be elevated on the outer side so as to give the roots a pleurodont 

 attachment. This is the case in the genus Pachi/rhizodus. Although a large 

 amount of material representing the forms referred to this family has come 

 under my observation, I have in no case seen any remains of si)inous fin-rays ; 

 in the pectoral fins in place, in two specimens of Empo, spines are wanting. 



The vertebral column is only known in Empo, where the caudal fin 

 embraces three and possibly four centra, being thus a little more heterocer- 

 cal than Salmo. 



The genera are readily distinguished by the following, among other 

 characters : 

 I. Premaxillary bone with several rows of teeth : 



Palatine teeth numerous, large ; all with pulp-cavity. . . . Stratodus. 

 II. Premaxillary with two rows of teeth : 



Maxillary bone short; dentary with equal large inner 



teeth and outer rows en brosse Empo. 



Maxillary bone very long; one row of equal dentaries. . . Pachi/rhizodus. 

 III. Premaxillary with one or no row of teeth : 



A large premaxillary fang ; anterior maxillary and den- 

 tary teeth enlarged ; cutting-edges not opposite ; 

 unsymmetrical Enchodus. 



Premaxillary toothless ; anterior maxillary and dentary 



enlarged ' Tctheodus. 



Large anterior tooth with a cutting-edge in front and a 



shorter one opposite and posterior F/umganodus. 



Owing to the fragility of many of the bones of the cranium, their char- 

 acters remain unknown. It is, however, certain that none of the above- 

 named genera present the prefronto-palatine articulation seen in the Sauro- 

 dontidce. For a similar reason, the structure of some of the tins remains 

 unknown. In some of the genera, the body is protected by scuta as well as 

 by scales. 



