54 PROCEEDINGS OF THE ACADEMY OF [1883. 



specimen was found in or on tlie Wando River, northeast of the 

 city of Charleston. 



This genus furnishes a first step in tracing backwards the phy- 

 logeny of tlie Sirenia. These animals doubtless present the same 

 phenomenon as that witnessed in the series of the Rhinoceroses, 

 Ruminants, and some others, viz., a gradual reduction in number, 

 and final extinction of the superior incisor teeth. In Rhj/tina 

 the extinction is complete ; in Halicore one remains. Dioplo- 

 therium with two, forms the passage to the primitive types, not 

 yet known, which possessed three. They are considerably 

 specialized in the present genus, and a reduction of size is to be 

 looked for in the first ancestral genera of the Sirenia. 



From the proportions of the parts preserved, the Dioplotheritim 

 manigauUi was rather larger than a dugong. 



A portion of a Sirenian pelvis said to have been procured from 

 the same locality, Wando River, was given me by Mr. Jacob 

 Geismar. It resembles considerably that of HaJitherium. A 

 portion of the ischium and pelvis is broken away, so that it is 

 not easy to determine positivel^^ whether there is an obturator 

 foramen or not. Their bases are, however, united for a considerable 

 distance beyond the acetabulum, and form a wide plate. The 

 ilium is a stout rod, expanding a little towards the crest, which is 

 broken away. The sacral articular surface is in two planes, one 

 the inner side, the other the posterior edge of the hone, and are 

 strongly impressed. The section of the shaft is subtriangular. 

 The acetabulum is small, has raised edges, and an irregular fossa 

 ligamenti teris notching its superior border. 



Measurements. 



Length from acetabulum to sacral face, exclusive, . '052 



Width acetabulum, ....... -027 



( anteroposterior, . . '018 



Diameter shaft ilium, ■< . „, _ 



' (transverse, . . . -Olo 



