314 



COMPARATIVE ZOOLOGY. 



Subclass I. — Marsipotoranohii. 

 The .Lampreys and Hag-fish have a persistent noto- 



chord, a cartilaginous 

 skull, no lower jaw, 

 a round, suctorial 

 mouth, horny teeth, 

 one nasal -organ, no 

 scales, limbs, or gill- 

 — , . V , A. arches. The gills are 



Pio. iiou.— l.uinpiey (Petromyzon Amerieanus). At- => 



lantic. pouch -like (whence 



the name of the class), and open separately. They ara 

 found both in salt and fresh water. 



Subclass II. — Pisces Proper. 



The true Fishes have two nasal organs, and well-devel- 

 oped jaws and gill-arches. Tiiere are four orders ; 



1. Elasmobranchii, having a cartilaginous skeleton, and 

 a skin naked or with placoid scales. The gill-openings are 

 uncovered ; and the month is generally under the head. 

 The ventral fins are placed far back; the pectorals are 

 large, in the Kays enormously developed ; and the tail is 

 heterocercal. Such are the Sharks, Kays, and Cliimsera. 



Fio. SS7.— Shark {Canhariaa vtdgarin), Atlantic 



