LOWER VERTEBRATES. 



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

 mon species on the east coast is Haia eriiiacea, which, for some vague reason, is called 

 among other names, the ' tobacco-box.' It rarely exceeds two feet in length. 21. 

 eglanteria, the brier skate, has the spines on the bod\- and tail very sharp. Haia Icevis, 



the smooth skate, oi- 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 sjDecies is R. binocnlata, of the 

 Pacific coasts, which grows to be six feet 

 in length ; its egg cases are proportion- 

 ately large, measuring nearly a foot in 

 length. More common in California is 

 the smaller R. iuornata. 



The family Tetgonid^ embraces the 

 sting-rays, so-called from the spines borne 

 on the base of the tail of some species, 

 which are capable of inflicting a severe 

 wound. These spines are 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 

 the Plagiostones. 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 poison 

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

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

 and many of the Scorptenids. 



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 pointed or tubercular. There are about ten 



genera, and about fift}- species, mostly 

 occurring in tropical sens, compara- 

 tively few straying into the more tem- 

 perate waters. Some occur in the 

 fresh waters of Central and South 

 America. All are ovoviviparous. 

 FIG. 66. - Spines of sting-ray. Most common On Our coasts are the 



species of Dasi/batiis (= Trygon), 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 



Fig. 65. — Rala Icevis, smootla slcate, barn-door skate. 



