ACEPHALA NUDA. 
Ill 
the Acephala Avith tubes is found in the fact that there is a double 
projection on one part of tlie cone, which really resembles the tAvo 
valA^es of the Acephala. Phe affinity betAA'een these little tubes and 
those Avhich envelope the tentacula of certain Terebella, formerly 
caused this animal to be referred to the Annelides. 
The species most knoAvn, — Asper. javanum,Mvivi.,Conch.,l. 
pi. 1 , f. 7, is seven or eight inches in length 
ORDER IL 
ACEPHALA NUDA f- 
The naked Acephala (a) are not numerous, and are sufficiently 
removed from the ordinary Acephala, to form a distinct class, Avere 
such a division considered requisite. Their branchiae assume various 
forms, l)ut are never divided into four leaflets ; the shell is replaced 
by a cartilaginous substance Avhich is sometimes so thin that it is as 
flexible as a membrane. We divide them into tAA^o families. 
FAMILY I, 
SEGREGATA(6). 
This family comprises those genera in Avhich the individuals 
that compose them are insulated and AAUthout any mutual organic 
connection, although frequently living in society. In the 
JBiphora, Bmg. — Thalia, Brown. — Salpa, U7id Dagysa, 
Gmelin, 
The mantle and its cartilaginous envelope are oval or cylindrical, and 
open at the tAVo extremities. Near the anus, the opening is trans- 
verse, Avide, and furnished with a valve Avhich permits the entrance 
of Avater, but not its exit ; near the mouth, it is simply tubular. Mus- 
* Add the Arrosoir a manchettes, Savig., Egyp. Coq. pL 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. 
(a) Or the Acephales sans coquilles oi 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 bis Aggreyh. — Eng. Ed. 
