THE STING RAYS 2921 



boat; and the danger is said to be the greatest in the case of a female accompanied 

 by its single offspring. We must not leave this family without referring to the 

 curiously-ridged quadrangular teeth from the Chalk described under the name of 

 Ptychodus, 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, sur- 

 rounded by a more finely-marked marginal area of variable width. They are ar- 

 ranged 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 



Apparently the most specialized 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 by 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 devel- 

 oped, 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, dan- 

 gerous not merely from the actual lesion, but apparently also from the presence of 

 some poisonous substance. In the larger kinds these formidable spines may be 

 as much as eight or nine 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 westward to America and eastward 

 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 abun- 

 dant 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 four to 

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

 a second genus, characterized 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 flat- 

 tened. The third genus {Urolophus) 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 (Pteropla tea}, of which there are some 



