91 

 VIL SIRENTA. 



FAMILIES. 



% 



I. Tail entire, rounded, and with the vertebrae towards last (i.e. 5-j-#); 

 sub-cylindrical and destitute of transverse processes. Intermaxillary 

 bones with the branches little prolonged backwards and with the anterior 

 portion nearly or quite straight. (Trichechoidea.') 



TEICHECHIDAE. (IX.) 



II Tail forked, and with the vertebrae (except the terminal) depressed and 

 provided with transverse processes. Intermaxillary bones (attypically) 

 with the branches prolonged backwards and with the anterior portion more 

 or less deflected. (Halicoroidea.) 



A. Teeth present, and in part at least functionally developed in the adult: 

 molars | to |x2 in number, but rarely present in full complement, the 

 anterior being gradually cast ; incisors in the upper jaw two (more or less 

 prominent) at least in the male. Teeth of the complete series at least 

 of Trichechidae M |r|, C , I |X2; the upper incisors only persistent, 

 the others as well as the canines being reabsorbed ; molars successively 

 increasing in size backwards. 



1. Molars mostly with two or three roots each (generally three-rooted 

 above and two-rooted below) ; and with crowns furnished with obtuse 

 tubercles arranged in transverse yoke-like eminences, and in the 

 posterior ones with an additional narrower tuberculated yoke behind 

 the principal ones. (Brandt.) 



HALITHEEIIDAE. (LXL) 



2. Molars with simple hollow roots (not separated from the crowns) ; 

 with crowns furnished with little prominent tubercles, few in number 

 (in the anterior teeth simple or double, in the rest three or four) not 

 forming yoke-like eminences, and early worn away and disappearing. 



HALICORIDAE. (LXII.) 



B. Teeth absent. (Intermaxillary lines with the apical portion produced 

 and simulating incisorial teeth. Manducation is only effected by a 

 very large palatine corneous plate, and by another opposed to it and 

 covering the very large and elongated symphysis of the lower jaw. 

 Brandt.) 



BHYTINIDAE. (LXIII.) 



BTTPEB-FAMIIY TEICHECOIDEA, 

 LX, TEICHECHIDAE. 



Genus. 



Trichechus Linn=!/ana<ws StoTr=Oxysiomus Fischer, 



'7 



