MARSIPOBEANCHII. 6 



the greater development of the dorsal fin in the latter. Species four 

 or more, found imbedded in the sand on various coasts. (Cirrostomi 

 Gtlir. viii, 513-514.) 



* Dorsal fold very low, nearly uniform ......................... BRANCHIOSTOMA, 1. 



1. BRArVCHIOSTOITIA Costa, 1834. 

 Lancelots. 



(Ampliioxus Yarrell.) 



(Costa, Ceuni Zoologici Napol. 1834, p. 49 : type Branchiostoma liibrlcum Costa = Limax 

 lanceolatus Pallas.) 



The characters of this genus are essentially those of the family as 

 given above, the little development of the fins constituting its chief dis- 

 tinctive character, (flpdyziaj gills ; <rr//.a, mouth. ) 



1. 12. csaribaeum Snndevall. American Lancelet. 



This species occurs in abundance, buried in the sand in shallow waters, 

 along the American coast, from the mouth of Chesapeake Bay to the 

 West Indies. It has never been fully compared with B. lanceolatum and 

 other species of the genus. 



(Branch iostoma caribceum Sundevall, Oefvers. Vet. Akad. Forhandl. 1853, 11.) 



CLASS IL-MARSIPOBRANCHIL 



(The Myzonts.) 



Skeleton cartilaginous; the skull imperfectly developed, not separate 

 from the vertebral column. No ribs, no true jaws, no limbs, no shoulder- 

 girdle, nor pelvic elements. Gills in the form of fixed sacs, without 

 branchial arches, six or more in number on each side. A single nasal 

 aperture. Mouth subinferior, suctorial, nearly circular. Heart with- 

 out arterial bulb. Alimentary canal straight, simple, without coecal 

 appendages, pancreas, or spleen. Generative outlet peritoneal. Verti- 

 cal fins with feeble rays, continuous around the tail. Naked, eel-shaped 

 animals, inhabiting all waters. (/jLapfffatov, a small pouch or purse; 

 , gills.) (Subclass Cyclostomata Giiuther, viii, 499-512.) 



ORDERS OF MARSIPOBRANCHII. 



* Nasal duct tube-like, with cartilaginous rings, penetrating the palate. 



HYPEROTRETA, B. 



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



