MAKSIPOBRANCHII. 6 



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

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

 Gthr. viii, 513-514.) 



* Dorsal fold very low, ncarl j^ uniform Branchiostoma, 1. 



1.— BRAXCHIOSTOiTIA Costa, 1834. 

 Lancelets. 



(Amjiliioxiin Yari'cll. ) 



(Costa, Ceuni Zoologici Napol. 1834, ii. 49 : typo BmncMostoma luhricum Costa = Limax 

 laneeolatus Pallas.) 



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

 given above, the little develoi^meut of the fins constituting its chief dis- 

 tinctive character. (^I'ipdy/ta, gills ; (rro/y.a, mouth. ) 



1. S. carH^secsm Suudcvall. — American Lancdct. 



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. 



(Brandiiufitoma caribci'uiii Simdevall, Oefvers. Vet. Akad. Forhaudl. 1853, 11.) 



Class II.-M ARSIPOBllANCHII. 



{The MyzonU.) 



Skeleton cartilaginous; the skull imperfectly developed, not separate 

 from the vertebral column. jSTo ribs, no true jaws, no bmbs, 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 

 api)endages, pancreas, or spleen. Generative outlet peritoneal. Yerti- 

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

 animals, inhabiting all waters, {p-afxri-iov, a small pouch or iiurse; 

 [:il>dr/ja, gill«-) (Subclass Cyclostomata Giinther, viii, 499-512.) 



ORDERS OF MARSIPOBIl.VXCini. 



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



Hyperotrkta, B. 

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



