380 



THE PLAGIOSTOMIA. 



Disk subcircular, about as broad as long, anterior margins slightly concave 

 opposite the eyes, outer margins and outer and hinder angles broadly rounded; 

 snout produced, sharp, length more than twice the interorbital width. Mouth 

 waved, curves rather abrupt, with two papillae at the bottom; teeth in 42 rows, 

 with a transverse ridge; spiracles as large as the eye. Ventrals subtriangular, 

 hinder rays shorter. Young, and rarely occasional adults, smooth. Older indi- 

 viduals with top of head and back of trunk covered with minute scales, either 

 uniform or with larger ones in a vertebral series of rounded or depressed tubercles. 

 This species is very variable, it may be with or without larger scales irregularly 

 placed in the vertebral series, or with or without a larger scale or group of several 

 at each side of the vertebral series above the shoulder girdle. Most specimens 

 have a median series of large depressed tubercles on the base of the tail in front 

 of the caudal spine, but these may be absent or may vary in number from one 

 to seven. The scales of the back vary from uniform, close-set to comparatively 

 few and scattered, or absent. In a large number of specimens from Penang the 

 females are a trifle the larger and the adults among them have a peculiar short- 

 ened and swollen end of the tail behind the spine. Generally the filamentary 

 extremity appears to be lost but sometimes a young female is found in which the 

 swelling is well advanced while the thin extremity is retained. Very young 

 females are hke the males. The tail is about one and one half times the length 

 of the body, varying to longer or shorter; it is without folds or rarely is with 

 rudimentary ridges (possible effects of contraction in preservation). 



East Indies. 



Dasybatus ponapensis. 



Trygon ponapensis Gunther, 1910, Siidsee fische, 3, p. 493, pi. 180. 



Disk subcircular or oval, nearly as broad as long. Snout moderate, with 

 slight prominence. Head rather large ; eyes prominent. Four tentacles on the 

 floor of the mouth. Mouth waved. Tail strong in the base, tapering, little 

 more than one and one half times the length of the disk, without dermal folds. 

 Skin smooth. Color uniform. Evidently a very young individual. 



Gunther says this form is very near his T. nuda, but differs in the oral 

 outline of the disk and lack of prominence at the tip of the snout. T. nuda 

 {imbricatus) has only two tentacles at the bottom of the mouth. 



Ponape. 



