314 



COMPARATIVE ZOOLOGY. 



Fig. 286.— Lamprey (Petromyzon Americanus). 

 lantic. 



At- 



Subclass I. — Marsipobranchii. 

 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- 

 arches. The gills are 

 pouch -like (whence 

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

 found both in salt and fresh w 7 ater. 



Subclass II. — Pisces Proper. 



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

 oped jaws and gill-arches. There are four orders : 



1. Elasmobranchii, having a cartilaginous skeleton, and 

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

 uncovered ; and the mouth is generally under the head. 

 The ventral tins are placed far back; the pectorals are 

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

 heterocercal. Such are the Sharks, Eays, and Chimaera. 



Fig. 287.— Shark (Carcharias vulgaris). Atlantic. 



