148 FIRST LESSONS m ZOOLOGY. 



rhomboidalj owing to the great development of the pectoral 

 fins. They swim close to the bottom, feeding upon shell- 

 fish, crabs, etc., crushing them with their powerful flattened 

 teeth. The smallest and most common skate of our north- 

 eastern Atlantic coast is Raja erinacea. It is one half of 

 a metre (twenty inches) in length, and the males are small- 

 er than the females. The largest species is the barndoor 

 skate. Raja Imvis, which is over a metre (forty-two inches) 

 long. 



The sharks have from the earliest geological ages (the 

 Silurian) remained the masters of the sea ; even now 

 there are species as big as whales, the great basking shark 

 being from thirty to forty feet in length, and the Ehino- 

 don over fifty. They need little protection beyond spines, 

 as in the sting ray and the dog-fish, etc., the exception 

 being the torpedo, a slothful ray which lies half buried 

 in the sand, and with its electrical battery strikes dumb 

 any intruder. 



LiTBKATTIRB. 



¥ishes in General.— Ounther : Introduction to the Study of Pishes. 

 London, 1880. — Jordan and Gilbert : Synopsis of the Fishes of North 

 America. 1883 . — Baird, Goode, etc. : Reports U. S. Commissioner of 

 Fish and Fisheries. — Goode's Game Fishes of the United States. — 

 Agasm and Vogt : Anatomie .des Salmones. 1846. — With the essays 

 of L. Agassiz, Storer, Gill, Cope, A. Agassiz, Kyder, Garman, etc. 



Sharks and Skates. — Muller and Henle: Systematische Beschrei- 

 bung der Plagiostomen. Berlin, 1841. — Hasse: Das natiirliche Sys- 

 tem der Elasmobranchier. Jena, 1879. — Wyman: Development of 

 Raiabatis. Mem. Amer. Acad., Boston, 1864. — Balfour: Monograph 

 on the Development of Elasmobranch fishes. London, 1878. 



