LOWER VERTEBRATES. 



Any detailed description of our species would prove dry reading. The most com- 

 mon species on the east coast is Raia erinacea, which, for some vague reason, is called 

 among other names, the ' tobacco-box.' It rarely exceeds two feet in length. Ji. 

 eglwderia, the brier skate, has the spines on the body and tail very sharp. Ruia Icevis, 



the smooth skate, or barn-door skate, is 

 our largest east-coast species, reaching 

 a length of four feet. In the young the 

 surface is spiny, but in the adult it is 

 nearly smooth. The largest of all the 

 American species is H. binoctilata, of the 

 Pacific coasts, which grows to be si.v feet 

 in length ; its egg cases are projiortion- 

 .itcly large, measuring nearly a foot in 

 li iigtli. More common in California is 

 the smaller 7?. inornata. 



The family Trtgoniu^ embraces the 

 sting-rays, so-called from the spines borne 

 f>n the base of the tail of some species, 

 which are capable of inflicting a severe 

 wound. These spines .nre the representa- 

 tives of the dorsal fin, which is otherwise 

 absent. The most anterior spine is the 

 functional one, and is used for offence 

 and defence. In the larger species it 

 may grow to be eight or nine inches long, 

 and is armed with barbs or serrations like 

 the teeth of a saw. As the teeth wear 

 out, the spine drops off, and is replaced 

 by the next one behind ; the succession 

 recalling that occurring in the teeth of 

 These barbs cut their way through the skin and flesh, the wound 

 they produce being very painful, swelling up as if poisoned. No trace of any ])oison 

 glands has been found, but it is jirobable that the mucus of the surface of the fish 

 possesses poisonous qualities, as it does in the case of the horned-pout, the weaver fishes, 

 and many of the Scorpoenids. 



Besides this character, the Trygonidse may be recognized by having the pectoral 

 fins confluent across the snout, no lateral folds on the long and slender tail, and the 

 pavement-like teeth usually more or less jiointed or tubercular. There are about ten 



genera, and about fifty species, mostly 

 occurring in tropical seas, compara- 

 tively few straying into the more tem- 

 perate waters. Some occur in the 

 fresh waters of Central and South 

 America. All are ovoviviparous. 



Most common on our coasts are the 

 species of Dagi/bati/s (^ Tri/ffO}i), the 

 fauna of the United States embracing six of the thirty known species. In the young 

 stages the skin is frequently smooth, but with growth it becomes more or less spiny 



, smooth skate, baru-iioor skate. 



the Plagiostones. 



Fig. 66. — Tail of sting-rav. 



