Fishes of the Western North Atlantic 335 



tin-like projections widely separated (Figs. 113, 116); teeth minute, in 

 many series. Mobulidae, p. 480. 



5 b. Anterior subdivisions of pectorals forming either one soft fleshy lobe 

 extending forward below front of head, or two such lobes joined together 

 basally; teeth large, in few series. 



6a. A single subrostral lobe or fin (Fig. 102). Myliobatidae, p. 433. 

 6 b. A pair of subrostral lobes or fins (Fig. 107). Rhinopteridae, p. 465. 



Family DASTATIDAE 

 Sting or Whip Rays 



Characters. Myliobatoidea with anterior portions of pectorals continuous along 

 sides of head, not separated off as subrostral lobes or fins; anterior part of head not 

 marked off from more posterior part of disc; crown only slightly elevated; disc not 

 more than 1.3 times as broad as long. Tail slender, tapering, much longer than disc 

 in many species; some species with a longitudinal membranous fold (or folds) above 

 or below, or both. Upper surface of tail armed in most species with one or more long 

 and sharp-pointed poisonous spines with serrate edges, flattened dorsoventrally and 

 attached rigidly to skin; tail spines directed rearward with tip lifted only slightly above 

 general contour of tail, the one close behind the other if there are two or more; mar- 

 ginal teeth of spine directed toward its base, their outer edges forming cutting edges 

 interrupted only by short interspaces between one tooth and the next. No rayed dorsal 

 or caudal fins. Eyes without expanded velum above pupil; eyes and spiracles on dorsal 

 surface. Nostrils separate from mouth, their anterior margins widely expanded and 

 confluent across a narrow isthmus, forming a single quadrate curtain with more or less 

 deeply fringed margin reaching rearward as far as front of mouth; outer posterior 

 margin of nostril expanded as a rounded lobe directed forward. Mouth straight or 

 slightly arched, on ventral surface considerably posterior to snout, the lower jaw more 

 or less indented centrally with the upper jaw curved rearward to correspond;^ floor 

 of mouth with a transverse row of several fleshy papillae of various lengths, their tips 

 often more or less swollen. Teeth small, in numerous series, closely crowded in bands 

 along jaws, rounded or with one or more cusps, often with ridges or tubercles. Upper 

 surface of disc and tail (apart from tail spine) smooth or variously roughened with 

 tubercles, thorns or prickles. Front of cranium weakly concave in most, perhaps straight 

 in some. Pelvis moderately arched forward in rounded contour but without median 

 process.* Surfaces of gill arches smooth inward from gill filaments. 



Remarks. The tail spine is a striking anatomical feature of all but one of the known 



3. This direction of curvature is opposite to that usual among Rajidae. 



4. In the freshwater genera Potamotrygon and Disceus the pelvis bears a long median process extending forward (Fig. 

 79B), and it is because of this that they were grouped bv Garman (Mem. Harv. Mus. comp. Zool., 36, 191 3: 415) 

 in the separate family Potamotrygonidae, which is accepted here for this same reason. In all other respects (other 

 than their freshwater habitat) they agree with the typical Dasyatidae. 



