dJfyA. 
4 ^^/' 
RHIXOBATIDiE. 
77 
(p etA^xxjS* 
name of ‘‘rostral teeth ”; the rostral region is thus seen to 
taper gradually, forming a long flattened blade. The 
endoskeletal cartilages are much crushed and broken, and 
at some distance from the base of the snout, where • the 
tapering decreases, they evidently occupy its entire width, 
from margin to margin. In addition to the ordinary 
median prolongation of the cranium itself, there is 
apparently a laterally-placed pair of large cartilages, 
corresponding to those of the existing Pristis, though it is 
not possible to determine whether they agree with the 
latter in structure. Purchased , 1884. 
Family RHXNOBATIDiE. 
Tail strong and long, with two well-developed dorsal fins; a 
caudal and a longitudinal fold on each side. Disk not excessively 
dilated, the rayed portion of the pectoral fins not being continued 
to the snout. No electric organ in the living forms. 
Genus RHXNOBATUS* Bloch (Schneider). 
[Schneider, ‘ Blochii Systema Ichthyologiae/ 1801, p. 358.] 
Syn. Euryarthra , L. Agassiz, Poiss. Foss. vol. iii. 1843, p. 382. 
Aellopos, G. von Munster, Nenes Jahrb. 1836, p. 581. 
Spathobatis, Thiofliere, Ann. Soc. Agric. Lyon [2] vol. i. 1849, 
p. 63. 
Body depressed, gradually passing into the tail. Cranial cartilage 
produced into a long rostral process, the space between the process 
and pectoral fin being filled by a membrane. Nostrils oblique, 
wide; anterior nasal valves not confluent. Teeth obtuse, with an 
indistinct transverse ridge. Dorsal fins without spine, both at 
a great distance behind the pelvic fins. Caudal fin without lower 
lobe. 
Spathobatis is described by Thiolliere as having the disk larger in 
proportion to the caudal region than in Rhinobatus , the pelvic fins 
being also more approached to the pectorals; but there seems to be 
an imperceptible gradation between the types, and it is thus con¬ 
venient, upon present evidence, to recognize but one genus. All the 
extinct species differ from the recent ones in the approximation of 
the pelvics to the pectorals, though this may sometimes be a false 
appearance, due to crushing during fossil ization. 
