LAMPKEYS. 347 



atlas 7M. — iiaarsi|)o6rand)iu 



{The IJampreys.) 



Skeleton cartilaginous, without ribs, limbs, shoulder 

 girdle nor pelvic elements; skull imperfectly developed, 

 without true jaws; a single median nostril; gills in the 

 form of fixed sacs, without branchial arches; gill sacs 

 typically seven on each side ; mouth nearly circular, suc- 

 torial; no scales; body elongated, eel-shaped; alimentary 

 canal nearly straight and simple; no arterial bulb. 



(Class VI. — Elasmobeaitchii, the Selachians, repre- 

 sented on our Atlantic Coast by many species of Sharks 

 and Skates, is here omitted, as its members are exclusively 

 marine, and it does not therefore come within the scope 

 of this treatise. Class VIII. — Leptooaedii, the Zian- 

 celets, is also omitted for the same reason. The latter 

 class contains, as far as now known, but two genera, 

 ■Epigonopterus and Amphioxus, with two or three species. 

 One of these, Amphioxtcs caribceus, Sundevall, occurs 

 along the coast of our South Atlantic States.) 



ORDERS OF MARSIPOBRANCHII. 



* Nasal duct a blind sac, not penetrating the palate. 



Htperoabtia, GO-. 

 ** Nasal duct penetrating the palate. Htpbkotbbta, page 347 

 GG. FAMILIES OF HYPBROARTIA. 



* Branchial sacs seven on each side • intestine with spiral valve. 



PETKOHTYZONTIDja;, 116. 



FAMILIES OF HYPEROTRETA. 



* One external apei-ture on each side of body, leading by six ducts 



to as many branchial sacs; no spiral valve; marine para- 

 sites, bmTowing into the bodies of other fishes. 



MyxinicUe, the Hag Fisli^i. 



