288 THE PLAGIOSTOMIA. 



the ventrals, a dermal fold along each side, and a moderately elongate caudal 

 in which the axis is not raised and the subcaudal fin without a lobe nearly equals 

 the supracaudal in development. Nostrils almost transverse; valves varying 

 in the different genera. Approaching the Rhinobatidae more closely in the genus 

 Syrrhina. 



The affinities of the genera placed in the Discobatidae are peculiarly di- 

 rected: — Discobatus is intermediate between the Rhinobatidae and the Narca- 

 ciontidae; Zanobatus, supposed to be oviparous, is nearer to the Raiidae between 

 it and the Rhinobatidae, while Platyrhinoides connects Discobatus and Zano- 

 batus though certainly viviparous. It may be that Zanobatus is not so differ- 

 ent in regard to oviparity as would seem to be the case from the discovery of an 

 egg in its shell within the oviduct. As figured the shell somehow has the ap- 

 pearance of one in which the embryo may be developed before extrusion. 



Rostrum short, broad, not half the length of the snout; two dorsal fin- 

 anterior narial valves not joined across the internarial space 



Discobatus (page 288) 



Rostrum extending to the end of the snout, pointed; two dorsal fins 

 anterior narial valves not joined across the interspace 



Platyrhinoidis (page 290) 

 anterior valves joined across the interspace . Zanobatus (page 291) 



Rostral cartilage absent; one dorsal fin . . Arhynchobatus (page 292) 



Discobatus. 



Discobolus Garman, 1881, Proc. U. S. nat. mus., 3, p. 523. 



Disk broad subcircular, or subtriangular with angles broadly rounded. 

 Pectorals very broad, forming the end of the snout, where they are rather nar- 

 rowly separated. Rostral cartilage short, broad, not extended half the distance 

 from the skull to the end of the snout, truncate and supplemented by soft pro- 

 longations, somewhat as in the Narcacionts. Nostrils nearly transverse, con- 

 nected with the mouth by a deep groove; anterior narial valve extended upon but 

 not crossing the internarial space. Eyes small. Spiracles close to the eyes, 

 with a cartilage at each side, without folds. Tail slender, about half the total 

 length. Ventrals close to the pectorals. Dorsals far behind the ventrals, small, 

 rounded. Caudals about equal, truncate; subcaudal not lobed. 



Japan; China. 



