ACEPHALA NUDA. HI 



the Acephala witli tubes is found in the fact tliat there is a double 

 projection on one part of the cone, wliich really resembles the two 

 valves of the Acephala. The affinity bctAveen these little tubes and 

 those which envelope the tentacula of certain Terebella, formerly 

 caused this animal to be referred to the Annelides. 



The species most known, — Asper. javanum, Mart., Conch. ,1. 

 pi. 1, f- 7» is seven or eight inches in length *. 



ORDER II. 



ACEPHALA NUDA f. 

 The naked Acephala (a) are not numerous, and are sufficiently 

 removed from the ordinary Acephala, to form a distinct class, were 

 such a division considered requisite. Their branchiae assume various 

 forms, Init are never divided into four leaflets ; the shell is replaced 

 by a cartilaginous substance which is sometimes so thin that it is as 

 flexible as a membrane. We divide them into two families. 



FAMILY I. 



SEGREGATA(6). 



This family comprises those genera in which the individuals 

 tliat compose them are insulated and without any mutual organic 

 connection, although frequently living in society. In the 



BiPHORA, Brug. — Thalia, Brown. — Salpa, and Dagysa, 

 Gmelin, 



The mantle and its cartilaginous envelope are oval or cylindrical, and 

 open at the two extremities. Near the anus, the opening is trans- 

 verse, wide, and furnished with a valve which permits the entrance 

 of water, but not its exit ; near the mouth, it is simply tubular. Mus- 



* Add the Arrosoir a manchettes, Savig., Egyp. Coq. pi. xiv, f. 9. 



t Since called by M. De Blainville Acephalophora heterobranchiata. As 

 to Lamarck, he makes a separate class of them, which he calls the Tunicata, and 

 which he places between his Radiata and his Vermes ; but these animals having a 

 brain, nerves, a heart, vessels, liver, &c. this arrangement is inadmissible. 



(j:^ (a) Or the Acephales sans coquilles of our author. — Eng. Ed, 

 (bj As this family has received no name from our author, we have been com- 

 pelled in conformity with the plan adopted from the commencement of the work, 

 to remedy the omission, for such we consider it, by the above word ; in the selection 

 of which we have been governed by that which the Baron himself affixes to the 

 second family, or his Aggregts. — Eng. Ed. 



