STING-RA YS. 



545 



family without referring to the curiously-ridged quadrangular teeth from the 

 Chalk described under the name of Ptyclwdus, which appear to indicate an extinct 

 type of eagle-ray. In these teeth the highly-polished crown is ornamented with 

 large transverse or radiating ridges, surrounded by a more finely-marked marginal 

 area of variable width. They are arranged in longitudinal rows ; the upper jaw 

 having the teeth of the middle row the largest, and those of the lateral rows 

 gradually decreasing in size : while in the lower jaw the middle teeth are rather 

 small, and the two adjacent rows the largest. 



The Sting- Rays, — Family Trygonid.e. 



Apparently the most specialised members of the entire group are the sting- 

 rays, in which the pectoral fins are continued uninterruptedly round the extremity 

 of the muzzle, so that the whole of the margin of the very wide disc is formed b}^ 

 these fins, in the centre of which is the more elevated head and body. The long 

 and slender tail, which is frequently armed with a serrated spine, is sharply 

 defined from the body ; and the median fins, if present at all, are either imperfectly 

 developed, or are modified into serrated spines. The forms with armed tails, to 

 which the name of sting-ray is alone strictly applicable, inflict very severe wounds, 

 dangerous not merely from the actual lesion, but apparently also from the pre- 

 sence of some poisonous substance. In the larger kinds these formidable spines 

 may be as much as 8 or 9 inches in length ; and, as they wear out, they are from 

 time to time shed and replaced by new ones growing from behind. Very 

 numerous in species, and arranged under several genera, the sting - rays are 

 most abundant in the seas of the tropics, although some range into temperate 

 waters. 



The typical genus includes some twenty-five species, one of which (Trygon 

 pastinaca) ranges from the south of England westwards to America and east- 

 wards to Japan. In this group the greatly elongated and tapering tail is armed 

 with a barbed arrow-shaped spine, while the skin is either smooth or dotted over 

 with tubercles, the nasal valves unite to form a quadrangular flap, and the teeth 

 are flattened. Mainly characteristic of tropical latitudes, these rays are most 

 abundant in the Indian and Atlantic Oceans, although some species are inhabitants 

 of fresh-water lakes in Eastern Tropical America. The rough ray (Urogymnus 

 asperrimus), of the Red Sea and Indian Ocean, which may measure from 4 to 5 

 feet in length from the head to the root of the tail, is the sole representative of 

 a second genus, characterised by the long tail being devoid of either fin or spine, 

 although sometimes furnished with a narrow fold of skin below. The whole 

 of the body is thickly covered with teeth-like tubercles, the teeth themselves 

 being flattened. The third genus ( Uroloplms) — in which the tail is of medium length, 

 furnished with a distinct terminal rayed fin, armed with a barbed spine, and some- 

 times with a rudimental dorsal fin, while the teeth are flattened — contains several 

 rather small-sized species from the tropical seas, and likewise an extinct one from 

 the Eocene rocks of Italy. A fourth genus (Pteroplatea), of which there are some 

 half-dozen representatives from temperate and tropical seas, is characterised by 

 the great width of the disc, which is at least twice as long as wide, and also 



vol. v. — 35 



