ORDER ACEPHALA NUDA. 125 
CLAVAGELLA, Lam., 
One of the valves is clasped by the tube, leaving the other 
however free. (Cl. echinata, Lam.) 
A single living species has been found in the madrepores of 
the Sicilian seas, which has been described by M. Audouin. 
Some naturalists think we should also place in this family 
the 
ASPERGILLIUM, Lam., 
The shell of which is formed of an elongated conical tube, 
closed at its widest extremity by a disk perforated with nu- 
merous small tubular holes; the little tubes of the outer range, 
being longest, form a kind of corolla about it. The reason 
for approximating them to the acephala with tubes is found 
in the fact that there is a double projection on one part of the 
cone which really resembles the two valves of the acephala. 
The affinity between these little tubes and those which enve- 
lope the tentacula of certain terebelle, formerly caused this 
animal to be referred to the annelides. 
The species most known (Asper. gavanens. Mart. Conch. I. 
pl.i. fi. 7.) is seven or eight inches in length. 
THE SECOND ORDER OF ACEPHALA. 
ACEPHALA NUDA 
Are very few in number, and are sufficiently remote from the 
ordinary acephala to constitute a distinct class, should such a 
separation be deemed expedient. Their gills assume various 
