DISCUSSION OF SPECIES AND THEIR DISTRIBUTION. 25 



vided -with two-rayed dorsals; skin more or less spinous; dentition ditieriiis in the two 

 sexes; the male usually provided with a differentiated patch of spines on each jiectoral. 



The genus Eaia is almost cosmopolitan, but most abundant in northern seas. 



In this genus are included the forms usually known by tlie name of Skate. About forty 

 species have been provisionally described, of which jjerhajts twelve are found in the Atlantic 

 basin below the 100-fathoni line. The genus has not yet l)een collected at a depth gieater 

 than (il2 fathoms. Of the seven species of L'aia occurring on the British coast, four at least 

 have been found in deep water. Of the nine species of the Atlantic coast of North America, 

 tive have been found in the depths. 



The Eays are believed to have been abundant in the Cretaceous and Tertiary periods, 

 but the species most characteristic of early geological times is allied rather to the forms 

 now living in shallow water than to those of greater deptlis. 



The Itays of the eastern and western Atlanti<' have not been compared with a suffi- 

 ciently large number of individuals at hand, and it is probable that when this shall be done 

 the number of species for the north Atlantic will be considerably reduced. 



The curious egg cases of the Rays, rectangular, black, leathery, with tubular flexible 

 tendrils at each of the four angles, popularly known as " devil's knitting sheaths" or " mer- 

 maid's purses," are well known to every stroller along the seashore. The large egg cases 

 of Raid kvvit are especially familiar. 



An unfamiliar form of egg, large, square, and with short tendrils, was found at various 

 depths off Newport in 1880, and young skates with extremely long tails were taken from 

 them. These have not yet been satisfactorily identified, but it will possibly be found that 

 they belong to Baia radiata. 



RAIA RADIATA, Donovan. (Figur()27.) 



liaja radiata, Donovan, Hist. Brit. Fi.sb.. v, \>\. 114, 1S20.— Storek, Rtijit. Fish. Mass., 201, 1839.— MiJLLER 

 and Henle, Plagiostomen, 137, 1841. — Domeril, Elasmobrauih., Tom. i, Ft. ii, .531, 1870. — Gunther, 

 Cat. Fish. Brit. Mus., viii, 460, 1870. — Challenger Rejiort, x.xii, 8. — Garman, Proc. Bost. Soc. Nat. Hist., 

 XVII, 1874, 178. — GoODE and Bean, Bull. Essex Inst., xi, 28. — Jordan, Bull, xvi, If. S. Nat. Mils., 41. 



Raja americana, De Kay, Zool. N. V., Fishes, 368, pi. 66, fig. 215, 1842. — Storer, Syn. Fish. North Amer., 260, 

 1846. 



Raja Iwvis, Storer, Hist. Fish. Mass.. 266 (description), 1867. 



Uaia with large spinous plates or bucklers, in addition to the spines on pectorals, head, 

 back, and tail found in K. ixrlhita. The.se are large, strong spines, with broad stellate or 

 shield-like bases. They are arranged as follows: One or two in front of each eye ; one on 

 each side between the eye and the spiracle; a pair on the slumlder, the smaller in front; 

 and fourteen or more forming a dorsal row, beginning just back of the head and extending 

 to the caudal. An irregular row of .spines on each side of the tail, separated from the 

 membrane by a band of shagreen; males with two or more rows of (daw-like spines on the 

 pectorals. Teeth with a htng, sharp point, rising from the middle and hooking backwards 

 in the male, bhmtish in the female; females larger than the males and more s])inous. 

 [Garman.) 



Baia radiata, which is not very uncommon at moderate depths off the New England 

 coast, but has not yet been found below the lOO-fathom line in the western Atlantic, has 

 been recorded by Collett from the region between Spitzt)ergen and Bear Island at a depth 

 of 127 to 259 fathoms, and also by Strom and Collett, in Throndhjem Fjord in 2.50 fathoms. 



RAIA ACKLEYI, Garman. (Figure 23.) 



Raja AcTclei/ijGAJiyiAS. Bull. Mus. Conrp. Zool., viii, 1881, 2.3.5. 



"Di.sk. including the ventrals, rhombic, longer than wide; anterior margins .sinuous; 

 po.sterior outline convex; tail moderate, depressed, with a narrow cutaneous Ibid on each 

 side, tapering. The angle formed by the snout is less than right. Rostral cartilage ratiier 

 slender, ilouth moderate, much curved; width one and two-thirds times in distance from 



