Jordan and Evermann. — Fishes of North America. 83 



Hemitrygon, (r)/n-, half; rpvymV, Trygoii, a dove, the same name alsoapplied to the sting rays): 

 a. Tail with a keel or wing-like expansion below only ; adult with stout bucklers on back ami 

 tail ; tail rough, more than twice length of disk. centruha, 121. 



Dasyatis : 



aa. Tail with a narrow keel or expansion both above and below. 

 h. Tail simply keeled above, with a wing-liko expansion below. 



c. Shoulder with 3 series of tubercles; tail less than twice length of disk. 



HASTATA, Vll. 



cc. Shoulder with less than 3 series of tubercles. 



d. Tail round, more than twice disk; back with strong tubercles; snout sharp. 



GYMNURA,123. 



bb. Tail more or less compressed, with a wing-like expansion above, a larger one below. 

 e. Skin more or less prickly in adult, with a median series of tubercles on back. 

 /. Tail more than J^ longer than disk. 



g. Disk subcircular, the snout prominent. Sabina, 124. 



gg. Disk subquadrangular, the suout blunt. longa, 125. 



ff. Tail not J^ longer than disk; disk subquadrangular, the snout blunt. 



DIPTERCRA, 126. 



ee. Skin nearly or quite smooth in adult; median line of back not prickly or with but 



1 spine. SAY, 127. 



Subgenus HEMITRYGON, Miiller & Henle. 

 121. DASYATIS CEXTRURA, (Mitchill). 

 (Common Sting Ray; Stingaree; Clam Cracker.) 



Disk quadrangular, about i wider than long. Anterior margins sinu- 

 ous, concave opposite the eyes, convex toward the slightly protuberant 

 snout and rounded outer angles ; posterior margin straighter, very little 

 convex ; inner convex ; hinder angles blunt. Ventrals truncate, with 

 rounded angles. Tail more than twice as long as the disk, much com- 

 pressed, rounded above, with keel or cutaneous exjiansion below, with 1 

 or more strong serrated spines at the termination of the anterior fifth of 

 its length, rough on all siaef with spines or tubercles. Till half grown, 

 the young are smooth; as they approach maturity, broad stellate-based, 

 conical-pointed, irregularly placed bucklers appear on the middle of the 

 hinder part of the back and on top and sides of the tail ; very large 

 examples have the central portion of the back closely mailed with small 

 flattened tubercles. Mouth arched forward, with 5 papilla' : teeth in 

 quincunx, blunt, smooth. Color on back and tail olive brown ; nearly 

 white below. From D. pastinaca, the common sting ray of Europe, which 

 this species resembles in shape, it is distinguished by the tubercles, by the 

 length and compression of the tail, and absence of all trace of keel or 

 expansion on its upper side. (Garman.) Coast of Maine to Cape Hat- 

 teras, abundant, reaching a length of 10 to 12 feet. (Kivrpor, spine ; olpa, 

 tail.) 



Rajacentrura, MiTCHiLL, Trans. Lit. Phil. Soc. N. Y., r, 479, 1815, New York. 

 Dasibatis cenlnira, Jordan & Gilbert, Synop.^is, 67, 1883. 



Subgenus DASYATIS. 



122. DASYATIS HASTATA, (DeKay). 



Disk quadrangular, about i wider than long ; anterior margins nearly 



straight, meeting in a blunt angle on the end of the snout, curved near 



the outer angle to meet the slightly convex posterior margins ; inner 



