MARSIPOBEAXCHII. 
3 
tbe greater developiueut of the dorsal fin in the latter. Species four 
or more, found imbedded in the sand ou various coasts. {Cirrostomi 
Gthr. viii, 513-514.) 
* Dorsal fold very low, nearly uniform Branchiostoma, 1. 
1.— BRAXCHIOSTOMA Costa, 1834. 
Lcmcclets. 
{Aviphioxus Yarrell.) 
(Costa, Ceuni Zoologici Xapol. 1834, x>. 49: type BrancMosloma luiricum Costa^ Limax 
lanceolaius 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. [iSpayyia^ gills ; o-ro/ja, month. ) 
1. B. CJas’iIl)aEMm Sundevall. — Amei-ican Lancclet. 
This species occurs in abundance, buried in the sand in shallow waters, 
along the American coast, from the month of Chesapeiike Bay to the 
West Indies. It has never been fully compared with B. Icmceolatum and 
other species of the genus. 
(Branehiostoma caribc^um Sundevall, Oefvers. Yet. Akad. Forhaudl. 1853, 11.) 
Class II.-MARSIPOBRANCHII. 
{The Mifzonts.) 
Skeleton cartilaginous; the skull imperfectly developed, not separate 
from the vertebral column. I^o ribs, no true jaws, no limbs, no shoulder- 
girdle, nor pelvic elements. Gills in the form of fixed sacs, without 
br.uichial arches, six or more in number on each side. A single nasal 
aperture. Mouth snbiuferior, suctorial, nearly circular. Heart with- 
out arterial bulb. Alimentary canal straight, simjile, without caecal 
appendages, pancreas, or spleen. Generative outlet peritoneal. Verti- 
cal fins with feeble rays, continuous around the tail. JTaked, eel-shai^ed 
animals, inhabiting all waters, {iiap^i-wv^ a small pouch or purse; 
^pdyyta, gills.) (Subclass Cjjclostomata Gunther, viii, 499-512.) 
ORDERS OF JDVRSIPOBRANCHII. 
* Nasal duct tube-like, with cartilagiuous rings, penetrating the palate. 
Hyperotreta, B. 
*■* Nasal duct a blind sac, not penetrating the i^alate Hyperoartia, C. 
