Fishes of the Western Nortli Atlcuitk 47 



some." In certain ovoviviparous species, all of the embryos in each uterus are enclosed 

 at first in a single pillow-shaped capsule, from which they are later set free into the 

 uterus, the walls of which are thickly set with villi. ^^ It is not known whether multiple 

 egg capsules of this sort occur in all ovoviviparous genera of the family. 



Genera. Two genera referred to this family by us have been made the basis of 

 a separate family by some authors,!^ partly because the rostral projection falls con- 

 siderably short of the tip of the snout in one of them {Platyrhind)., and probably in 

 the other (^Zanobatus^*), whereas in all others it extends to the snout's extremity. In 

 this respect, Platyrhina bears much the same relationship to the hard-nosed Guitar- 

 fishes, as exemplified by Rhinobatos or Plalyrhinoidis, as do the soft-nosed Skates (Psam- 

 mobatis^ Sympterygia, Brevirajd) to the hard-nosed Skates {Raja), with which they are 

 united in a single family (Rajidae) by common consent. Therefore, we see no reason 

 for their separation on this basis. ^^ 



Key to Genera 



I a. Snout wedge-shaped, ranging from obtusely so to slenderly prolonged; tips of 

 anterior rays of pectorals falling considerably short of tip of snout. 

 2 a. Lobe-like expansion of anterior margin of nostrils far apart from each other 

 and from upper lip. 



3 a. Lobe-like expansions of anterior margin of nostrils covering only a narrow 

 belt midway of nasal opening. 



4 a. Posterior margin of spiracles with one or two well marked ridges or 

 folds; nostrils more or less oblique; inward extension of lobe-like 

 expansion of anterior margin of nostrils ending some distance out- 

 ward from inner corner of nostril. Rhinobatos Link 1790, p. 50. 

 4b. Posterior margin of spiracles without folds; nostrils transverse; in- 

 ward extension of lobe-like expansion of anterior margin of nostril 

 crosses inner angle of nostril. Aptychotrema Norman 1926. 



Australia (two species).^* 



11. Muller (Denkschr. Akad. Wiss. Berl. [1840], 1842: 249, pi. 6, fig. 2; also separate, Ueber den flatten Hai, 1842: 

 62, pi. 6, fig. 2) found in the uterus of a Zanobatus schoenUinii an egg with a horny capsule, much resembling the 

 eggs of the scyliorhinid Sharks; its shape suggested that embryonic development takes place after the eggs are 

 laid, since it was provided with two coiled tendrils at one end. 



12. This type of ovoviparity has been reported for the Australian Aptychotrema banksii (MiiUer and Henle) 1841, where 

 each of the two capsules (one per uterus) contained 7-8 embryos (Haacke, Zool. Anz., 8, 1885: 48S, as R/iinobatus 

 'vincentianus, n. sp.); also for Trygonorhina fasciata (likewise Australian), in which each capsule contained two 

 or three embryos. For illustrations of the egg capsule and of the villous uterine wall in the former, see McCulloch 

 (Biol. Result. Fish. F. I. S. 'Endeavour', 5, 1926: 158, figs. 1-4, as RAinobatus banksii), and Whitley (Fish. Aust., 

 I, 1940: 172, fig. 196, as Aptychotrema 'vincentiana). For an account of the embryonic stages of Rhinobatos halai'i 

 and Khynchobatos djiddensis, see Melouk (Publ. Mar. bid. Sta., Ghardaqa, Fouad I Univ., 7, 1949). 



13. Discobatidae (Garman, Mem. Harv. Mus. comp. Zool., 36, 1913: 258); Platyrhinidae (Fowler, BuU. U.S. nat. 

 Mus., 100 [jj], 1941: 289). 



14. Norman (Proc. zool. Soc. Lond., 1926: 982) writes "as far as I am able to judge from a partial dissection of this 

 very young example, the rostral cartilage does not reach the extremity of the snout." 



15. In this we follow Norman's Synopsis (Proc. zool. Soc. Lond., 1926: 941). 



i6. The characters used by Norman (Proc. zool. Soc. Lond., 1926: 977) in separating the genus Aptychotrema from 



