462 FISHES CHAP. 
which they live, and thus concealed, small Fishes, Crustaceans, 
and other organisms are lured unsuspectingly within the reach of 
the comparatively inactive and sluggish Ray. From the ventral 
position of the mouth the Ray cannot at once seize its prey, but 
the Fish darts over its victim and covers it with its body, and 
then readily devours it. The sexes are usually distinguished by 
secondary sexual characters, which take the form of differences in 
size and coloration, in the dentition, and also in the presence and 
position of patches or rows of specially modified dermal spines on 
the dorsal surface (Fig. 264). Some of the larger species reach 
a great size, the disc measuring 7 to 8 feet in width. <A few 
species range into deep water. &. mamillidens, a uniformly jet- 
black species, has been obtained from a depth of 597 fathoms in 
the Bay of Bengal,’ and &. abyssicola from 1588 fathoms off 
Queen Charlotte Islands, British Columbia.” The following are 
British species: the Thornback (f. clavata); the Spotted Ray 
(hk. maculata); the Painted Ray (A. microcellata); the Starry 
Ray (R. radiata); the Cuckoo or Sandy Ray (£&. cireularis) ; 
the Skate (Rf. batis); the Flapper Skate (2. macrorhynchus); the 
White Skate (2. alba); the Long-nosed Skate (A. oxyrhynchus) ; 
and the Shagreen Ray (R. fullonica).? Most of the species are 
of some economic value as food Fishes. Psammobatis, with a 
circular dise, frequents the southern coasts of South America, 
and Platyrhina the coasts of India, China, and Japan. 
The family ranges from the Upper Cretaceous, in which, as 
well as in different Tertiary deposits, it is represented by species 
of Raia. An extinct genus, Cyclobatis, with a circular or oval 
disc, occurs in the Upper Cretaceous of Mount Lebanon. 
Fam. 4. Tamiobatidae.—The systematic position of the only 
representative of this family, Z’wmiobatis vetustus,* from the 
Devonian or Lower Carboniferous of Kentucky, is very uncertain, 
but im some respects this unique type seems to be intermediate 
between the modern Sharks and the Rays. 
Fam. 5. Torpedinidae (Electric Rays).—A disc is formed as in 
the Raiidae, but it is sub-circular in shape rather than rhombic, 
and in the nature of its endoskeletal supports it is im some 
respects unique. Its semicircular anterior margin is supported 
1 Alcock, Ann. Mag. Nat. Hist. (6), iv. 1889, p. 380. 
? Jordan and Evermann, op. cit. p. 76. 
° Day, op. cit. p. 336. 4 Zittel, op. cit. p. 41. 
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