THE TRUE RAYS OR SKATES 



2917 



JAWS OP MALE (A) AND FEMALE (B) THORNBACK 

 SKATE. 



THE TRUE RAYS OR SKATES Family 



Represented by upward of seven British species, all of which belong to the 

 typical genus, the true rays are characterized by the broad and rhombic form of the 

 disc, the skin of which is generally marked with tooth-like rugosities. The tail 

 has a longitudinal fold on each side, the degree of development of the median fins 

 is variable, and the rayed portion of the pectoral fins extends to the muzzle. With 

 the exception of occasional traces in the tail, electric organs are wanting. Of the 

 typical genus we take as a well- 

 known example the common Brit- 

 ish thornback (Raia davata}, of 

 which two examples are shown in 

 the illustration. In this genus the 

 tail is very sharply defined from the 

 disc, which is generally covered 

 with rugosities; the pectoral fins 

 stop short of the extremity of the 

 muzzle; the pelvics are deeply 

 notched, with a stout front carti- 

 laginous ray; the tail carries two 

 dorsal fins, and the caudal is rud- 

 imentary, or wanting. Most of 

 these skates are remarkable for presenting sexual differences, which in the 

 thornback and several other species display themselves in the dentition, the 

 teeth of the males being sharp and pointed, while those of the opposite sex 

 are blunt and flattened. Whereas the males of all the species are armed 

 with patches of claw-like spines lying in grooves on the upper surface of the 

 pectoral fins, and frequently also on the sides of the head, the females of 

 some species have a kind of buckler of asperities on the disc, which is wanting 

 in the other sex. In other cases the variation takes the form of a difference in 

 color. The numerous members of this genus are in the main characteristic of the 

 cooler seas, and while they are more abundant in the Northern than in the Southern 

 Hemisphere, some of them approach nearer to the Arctic and Antarctic Circles than 

 is the case with any other rays. The flesh of all of them is eatable, that of many 

 species being commonly sold as an article of food. The common skate (Raia 

 baits'} , which is ordinarily of from two to four feet in length, is grayish white in 

 color, with black specks, the whole upper surface being more or less granulated. 

 Buckland records an unusually large specimen which weighed ninety pounds. The 

 thornback takes its name from having the whole of the upper surface studded at 

 intervals with the above-mentioned claw-like spines; the tail being also armed with 

 longer spines, of which a row runs along the middle of the back. The prevailing 

 color of the upper surface is brown, with numerous lighter spots, while beneath it 

 is pure white. Fossil skates of this genus range through the Tertiaries to the 



