STING-RA VS. 
545 
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, 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 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 
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 (Try g on 
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 ( 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 ( 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 
