Fishes of the IVestern North Atlantic 133 



Key to Families 



1 a. Two dorsal fins. Rajidae, p. 133. 

 lb. Only one dorsal fin, or none. 



2a. One dorsal fin; disc prickly; inner margins of pelvics separate from tail. 



Arhynchobatidae. 



New Zealand.' 

 2b. No dorsal fin; disc without prickles or thorns; inner margins of pelvics fused 

 with tail nearly or quite to their tips. Anacanthobatidae, p. 327. 



Family RAJIDAE 



Characters. Tail only moderately slender, at most not more than about 2.0 times 

 as long as body sector; rounded above, flattened below, with a narrow dermal fold 

 along each side. Two dorsal fins. Pelvics with outer margins ranging from only weakly 

 concave to so deeply so that anterior division of fin forms a limb-like structure entirely 

 detached from the posterior part, three-jointed and (as it seems) separately movable. 

 Orbits prominent, rising considerably above general level of head. Eye in some with 

 expanded velum above the pupil. Spiracle close behind eye. Nostrils more or less 

 oblique, their inner ends actually separate from mouth though superficially connected 

 with outer corners of latter by shallow furrows; their expanded inner (anterior) margins 

 joined across a broad isthmus in front of mouth and expanded rearward on either side 

 as an extensive rounded curtain, smooth or more or less deeply fringed, roofing all but 

 outer (anterior) ends of nasal apertures and reaching back to either corner of mouth; 

 posterior margin of outer (exposed) part of nostril also expanded as a narrower flap, 

 smooth-edged in some species but more or less deeply fringed in others, capable of 

 assuming a more or less ring-like or tubular form, depending on the state of con- 

 centration. Mouth moderately broad, transverse, its median sector more or less bowed. 

 Teeth numerous, flattish to rounded or with one sharp cusp; arranged either in quin- 

 cunx or in looser transverse series; several rows in function simultaneously. Skin of 

 upper surface of disc and tail more or less rough with small prickles, larger thorn-like 

 denticles, or both, but without serrate tail spines; lower surface either smooth or with 

 prickly areas, in some cases with a few thorns. Pectoral girdle with a scapular element 

 fused with the upper side of vertebral column. Pelvis nearly straight transversely, with 

 a longer or shorter process extending forward from the outer corner at each end (Fig. 



2 7 A). Front of cranium with or without a rostral projection (rostral cartilage), the 

 midline of snout stiff^er or softer accordingly.* Anterior rays of pectorals either close 

 together at tip of snout (when rostral cartilage is short or lacking) or separated there 

 by rostral cartilage. Characters otherwise those of the suborder (p. 132). 



3. Arhynchobatis Waite 1909 is placed by Fowler (Bull. U. S. nat. Mus., 100 [/j], 1941: 333) as a subfamily (Arhyn- 

 chobatinae) of Platyrhinidae, which we refer here to the Rhinobatidae (p. 47). It is described (Waite, Rec. Canter- 

 bury [N. Z.] Mus., I [2], 1909: 150, pi. 20) as not having a rostral cartilage and its resemblance in this respect to 

 Psammobalis among Rajidae is pointed out. 



4. For a general account of the head skeleton and comparison with other batoids, see Holmgren (Acta Zool. Stockh., 

 22, 1941 : 52, 64, 65). 



