CIRROSTOMl. 513 



Subclass VI. LEPTOCARDII. 



Skeleton membrano-cartilaginous and notochordal, 

 ribless. No brain. Pulsating sinuses in place of 

 heart. Blood colourless. Respiratory cavity con- 

 fluent with the abdominal cavity ; branchial clefts in 

 great number, the water being expelled by an opening 

 in front of the vent. Jaws none. 



Cfi". Miiller, Abhandl. Ak. Wiss. Berlin, 1846, p. 198. 



One family only — 



CIRROSTOMI. 



Amphioxini, Miiller, I. c. p. 20-4. 

 Cirrostomi, Oiven, Anwt. Vertcbr. i. p. 9. 



Characters of the single genus. 



1. BRANCHIOSTOMA. 



Branchiostoma, Costa, Ccnni Zool<>(/ici Xapol. 1834, p. 49. 

 Amphioxus, Yarrell, Bi-it. Fish. 183(J, p. 4U8. 



Body elongate, compressed, scaleless, limbless. Mouth a longi- 

 tudinal fissure, with subrigid cirri ou each side, inferior. Vent at a 

 short distance from the extremity of the tail. A low, rayless fin- 

 like fold runs along the back, round the tail, past the vent, to the 

 respirator}- aperture. Eye rudimentarj*. Liver reduced to a bhnd 

 sac of the simple intestine. 



One genus only, occupying the lowest scale in the class of verte- 

 brata. Found imbedded in sand on many coasts of the temperate 

 regions of the northern and southern hemispheres ; also in Brazil. 



1. Branchiostoma lanceolatum. 



Lancelet. 



Limax lanceolatus, Pall. Spicil. Zool. x. p. 19, tab. 1. fig. 11. 



Bnmchiostoma lubricum, Costa, I. c, aud Faioi. Regn. Xapol. Peso. ; 



Midi. Abhandl. Ak. Wiss. Berl. 1842, pp. 79-116, pis. 1-5. 

 Amphioxus lanceolatus, Yarrell, Brit. Fkh. 1830, p. 4(38, or 2nd edit. 



ii. p. 018, or 3rd edit. i. p. 1 * ; Couch, in Charlesworth's Mag. Nat. 



* Not the specimen from Moray Firth, wliich was probably a young Mt/xim ; 

 and the article by Mr. Wildo refers to a Salpa. 



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