148 REPORT OF STATE GEOLOGIST. 



Class 1. CYCLOSTOMI. 



THE HAG-FISHES AND LAMPREYS. 



Skeleton entirely cartilaginous, membranous and notochorclal. Verte- 

 bral axis not divided into distinct vertebrae. No ribs. No paired fins. 

 Anterior portion of the head containing large cartilages which support 

 the suctorial disk. No lower jaw developed, nor any evident upper jaw\ 

 Mouth and suctorial disk of adults armed with horny teeth. Nasal organ 

 single, opening in the midline of the upper surface of the head. Gills 

 sac-like, six or more on each side, openiug usually by as many holes in a 

 line along the sides of the body, occasionally into a canal which opens 

 far back on the ventral surface. Dorsal and anal fins -with rays, and 

 meeting around the end of the tail. 



This class contains a number of very remarkable animals, some of 

 which inhabit the ocean, others the waters of rivers and lakes. They 

 are parasitic on other fishes, seizing them by means of the suctorial disk, 

 then with the horny teeth, rasping away the flesh and sucking the blood 

 of their victims. Some of the marine species even burrow into the 

 bodies of the larger fishes. 



The two succeeding orders of this class are recoguized : 



A. Nostril close to the border of the disk ; the nasal duct openiug 

 behind on the roof of the mouth. Hyperotreta. 



A A. Nostril opening just in front of the eyes; the duct terminating 

 behind in a blind sac. Hyperoartm, p. 148. 



All our species belong to the last-named order. 



Order 1. HYPEROARTIA. 



Nasal organ with its external openiug placed on the top of the head, 

 just in front of the eyes ; the duct terminating behind in a flask-shaped 

 sac, which lies at the base of the skull ; eggs small. 



This order contains only a single family, the Petromyzontidtc : 



Family PETROMYZONTID.E. 

 THE LAMPREYS. 



Body eel-like, scaleless and slippery; anteriorly cylindrical, com- 

 pressed behind. Dorsal and anal meeting around the tail, the dorsal 

 more or less notched. Sucking disk armed wdth horny teeth in the 

 adults, unarmed in the larval stage ; surrounded with a fringed border. 

 Tongue with teeth. Gill openings seven in number along each side. 



