BATOIDEI. 329 



Group II — Batoidei. 



Spiracles present : gill-openings in five pairs, and on the ventral surface of the 

 hody. Body depressed, forming (due to largely -developed pectoral fins) a vwre or 

 less flat disk, and having usually a slender and elongated tail. Dorsal fins, when present, 

 on the tail : anal absent. 



Rays and skates exist in considerable numbers in tlie seas around our coasts, 

 and some attain to a large size. Their skins, used for sbagreen, are considered 

 superior to those of sharks, owing to the scales being of somewhat larger dimen- 

 sions. The horny case which encloses the foetal ray are more square in form than 

 what are observed in sharks, while the projections at the corners are wanting in 

 the long tendrils. In August, 1881, I observed an old man at the Barbican at 

 Plymouth removing the livers from rays and skates, from which he extracted the 

 oil, which he stated to be much used by shoemakers, especially in the manufacture 

 of cobbler's wax. It is also employed for boats, and a variety of other purposes. 



Synopsis of Families. 



I. ToepedinidjE. — Trunk a broad smooth disk. Generally both dorsal and 

 caudal fins. An electric organ. Page 330. 



II. Raiid^;. — Trunk a broad and generally rough disk. Pectoral fins extend 

 on to the snout. A fold of skin along either side of the tail ; no serrated caudal 

 spine. No electric organ. Page 334. 



III. Tetgonidji.- — Pectoral fins extend on to and are confluent at the snout. 

 No fold along the side of the tail, which latter is usually armed with a serrated 

 spine. Page 350. 



IV. Mtliobatid^. — Pectoral fins do not extend on to the side of the head : 

 snout with a detached pair of fins. Page 352. 



Montagu (Wern. Mem. 1815) observed upon how the colours of these fish vary, 

 and how sexual distinctions had been overlooked. The males are provided with 

 claspers, " a most curious structure, hanging pendant one on each side of the tail, 

 between it and the anal fins ; the testes are enclosed at the base of these, not 

 obvious but by dissection. What accompanies this truly masculine distinction is 

 a series of large, reclined, hooked spines, never to be found in the other sex, and 

 which begin to show themselves early in all the species hitherto examined. These 

 are placed in four distinct series, one on each shoulder or fore-part of the wing or 

 pectoral fin, and one at each angle of the wing." They lie with their points 

 reclined inwards in two, three, and sometimes four parallel lines, the number in 

 each row being dependant on age. They may be developed during the breeding 

 season, at which period, observes Darwin,* they are brought into use for prehensile 

 purposes, by doubling inwards and downwards the two sides of the body. In some 

 species, as Eaia clavata, the females have their backs studded with large, 

 hook-formed spines. The teeth of the different sexes usually show considerable 

 differences. 



» " Descent of Man," p. 331. 



