Fishes of the IVestern North Atlantic 43 



Suborder RHINOBATOIDEA 

 Guitarfishes 



Characters. Trunk anterior to cloaca ranging from shark-like to disc-like in form. 

 Snout without blade-like extension, its edges without teeth. Tail sector much stouter 

 than in any other batoids excepting the Sawfishes (p. 18) and Torpedo Rays (p. 80), 

 sharply marked off from body sector in disc-shaped species but not in those with a more 

 shark-like form. Attachment of anterior expansions of pectoral fins to sides of head 

 extending only a little past mouth in some, for various distances thence forward in 

 others, and nearly to midline of snout in extreme cases. Two well developed dorsal fins, 

 the first originating much closer to tips of pelvics than to tip of tail. Caudal fin well 

 developed. Pelvics with outer margins convexly rounded and wholly separate from 

 pectorals. 



Eyes with an obscure fold of skin below. Nostrils entirely separate from mouth 

 in most cases but connected with it by a broad shallow furrow^ in some. Corners of 

 mouth without voluminous furrows extending rearward. 



Body and fins closely covered with small dermal denticles of various shapes, skin 

 of upper and lower surfaces mostly concealed except for the interbranchial region, which 

 is largely or wholly naked in some cases. Back more or less thorny along midbelt, on 

 shoulders, around eyes and spiracles, and over rostral cartilage in some species. Tail 

 without a serrate-edged spine. 



Anterior margin of cranium with a single unbranched rostral projection^ extending 

 nearly or quite to tip of snout in most but falling considerably short of it in Platyrhina 

 (p. 50), in which it is continued forward by soft ligamentous strands. In most species 

 the separate antorbital cartilages do not take any part in supporting the anterior part 

 of the head; in Platyrhina they extend forward beyond the orbital region but fall short 

 of the anterior margin of the disc. Tips of branchial rays either cylindrical or some- 

 what expanded, less so than in the Torpedo Rays. Dorsal and caudal fins supported 

 basally by short cartilaginous radials and distally by much more numerous fine horny 

 rays (ceratotrichia) in double series. Pectoral and pelvic fins without horny rays, the 

 cartilaginous radials extending outward to margins of pectorals, nearly to margins of 

 pelvics. Pelvis transverse, either with or without a small anterior process at either end. 

 Anterior and posterior surfaces of gill arches inward from gill filaments with a series 

 of low, firm, widely-spaced knobs. No electric organs. Development ovoviviparous in 

 most species, perhaps oviparous in a few (p. 47, fn. 11).* 



Remarks. The rhinobatoids present nearly an unbroken series as regards shape of 

 disc, length and shape of snout, degree of forward extension of pectorals, position of 



1. This connection between nostril and mouth is described by Garman (Mem. Harv. Mus. comp. Zool., 36, 1913: 

 289) as "deep" for Platyrhina sinensis (Bloch and Schneider) 1801 ; actually we found that it is shallow though broad 

 in an excellently preserved specimen of that species from Japan. 



2. Commonly termed "rostral cartilage," although it is continuous with the cranium. 



3. For an account of the embryonic stages of RJiyncfiobatos djiddensis, see Setna and Sarangdhar [Rec. Indian Mus. 

 (1948), 46 (1-4), 1949: 18-23, figs. 7-8. pl- I. %-4]- 



