DISCUSSION OF SPECIES AND THEIR DISTRIBI'TION. 



25 



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

 sexes; the mak' usually provided with a differentiated patch of spines on each pectoral. 



The genus Rata is almost cosmopolitan, 1ml most abundant in northern seas. 



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

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

 basin below the 100 fathom line. The genus has not yet been collected at a depth greater 

 than oil* fathoms. Of the seven species of Baia 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, 

 five have been found in the depths. 



The Bays 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 depths. 



The Bays of the eastern and western Atlantic 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 Kays, 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 Baia Iwvis 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. (Figure 27.) 



Raja radiata, Donovan, Hist. Brit. Fish., v, pi. lit, 1820. — Stoker, Rept. Fish. Mass., 201, 1839.— Muli.er 

 ami Heni.e, Plagiostomen, 137, lxll.— Dumeril, Elasmobranch., Tom. i, Pt. n, 531, 1X70.— Ginther, 

 Cat. Fish. Brit. Mus., vm, 160, 1870. — Challenger Report, xxn, 8.— Garman, Proc. Bost. Soo. Nat. Hist., 

 xvn, 1874, 178.— Goode and Bean, Bull. Essex Inst., xi, 28.— Jordan, Bull, xvi, IT. S. Nat. Mus., 41. 



Raja americana, Iln Kay, Zool. N. V., Fishes, 308, pi. 66, fig. 215. 1842. — Storer, Syn. Fish. North Amer., 260, 

 1846. 



Raja Icevis, Stoker, Hist. Fish. Mass., 266 (description). 1867. 



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

 back, ami tail found in B. ocellata. These 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 shoulder, 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 claw-like spines on the 

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

 in the male, bluntish in the female; females larger than the males and more spinous. 

 [Garman.) 



Baia r«<ii<tt<i, 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 Spitzbergen and Bear Island at a depth 

 of 127 to 2.59 fathoms, and also by Strom and Collett, in Throndhjem Fjord in 250 fathoms. 



RAIA ACKLEYI. Garman. (Figure 23.) 

 Raja Aokleyi, Carman - . Bull. Mus. Comp. /.<>•">!. . vm, 1881, 235. 



"Disk, including the ventrals, rhombic, longer than wide; anterior margins sinuous; 

 posterior outline convex; tail moderate, depressed, with a narrow cutaneous fold on each 

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

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



