CONTRIBUTIONS TO NORTH AMERICAN ICHTHYOLOGY - IV. 



$ Skull without iiirialiranr hours (a "rudiinciital opercnlarbone" in fhinm ,-a ); 



^ill- not 1'ivr. the liraiirliial openings slii-likr, usually srvcral in number; 



c\o>k<'k'itm jilacoid, soinrt imcs olisol. !< : --> few ami lar.nv. 



Ki.ASMor.KAXt nn. ::. 

 }{ Skull with mrmbraii" hones; j^ills 1'ivo ; branchial openings a single slit on 



each side, soinri imcs rontlurn; ; exoskolrton various, not plaroid; 



comparatively small and IIUUHTOUS .......................... PISCES, 4. 



CLASS I.-LEPTOCARDII. 



(The Lancelots.) 



Skeleton membrane-cartilaginous; skull undeveloped, with tlie noto- 

 chord persistent and extending to the anterior end of the head. Brain 

 not dill'erentiated. Xo heart; the function of the heart being performed 

 by pnKatingsinuses. Blood colorless. Respiratory cavity confluent with 

 the cavity of the abdomen; branchial clei'ts in great number, the water 

 being expelled through an abdominal pore in front of the vent. Jaws 

 none; the month a longitudinal fissure, with cirri on each side. 



SiiKill marine animals highly interesting to the zoologist as exhibiting 

 the lowest degree of development of the vertebrate type. The class 

 includes but the single order Cirroxlomi. (/sw?, thin; xapuia, heart.) 

 (Subclass Lrjtt.ocardii Giinther, viii, 513-514.) 



ORDER A.-CIRROSTOMI. 



(The 



This order is equivalent to the family BranohiostomatidtB. (Latin, 

 cirrus, a lock of hair; <77/'-a, mouth : the mouth being surrounded by u 

 tViiige of cirri.) (Cirrostouti (iiinther, viii, 513-51-4.) 



FAMILY I. BKAXCIIIOSTOMATID^E. 

 (The Lancelctx.} 



Body elongate, cuiiqiressed, naked, colorless, with no fins, except a 

 ra\ less fold extending along the hack, around the tail, past the vent, to 

 the abdominal pore. Month interior, appearing as a longitudinal fis- 

 sure. surrounded 1>\ conspicuous, rather still' cirri. Kye rudimentary. 

 Liver reduced to a blind sac of the simple intestine. 



ra two, Branchioatoma and Epigonopterus, differing chiefly iu 



