CONCHOLOGICAL MANUAL. 
AB/SIA. Leach. Liruorrya, Sow. Fam. Pedunculated Cirri- 
pedes, Lam. 
ACA’MAS. Mont. Bexemnires multiforatus, Bl. A species 
described as being terminated at the apex by a stellated perfora- 
tion. This is supposed to have been described from a broken spe- 
cimen, as no fossil is now known agreeing with the description. 
ACAR’DO. Commergon. Described from a pair of bony plates, 
placed between the vertebrze of the whale, and mistaken for a 
bivalve shell, destitute of a hinge. 
ACAS'TA. Leach. Order, Sessile cirripedes, Lam. Batanus 
Montagui, &c. Sow. Separated from Balanus, on account of 
the cup-shaped process at the base, but re-united by Sowerby, 
who shews that this is a mere accidental circumstance, resulting 
from the situations in which the shells acquire their growth. 
The Acastz are found imbedded in sponges. Hz. Acasta Mon- 
tagul, fig. 26. 
ACA’VUS. Montf. Fam. Limacinea, B]. Colimacea, Lam. A divi- 
sion of the genus Hetrx which may be considered synonymous 
with De Ferussac’s sub-genus Helicogena. De Montfort has 
figured H. Hemastoma. See fig. 267. 
ACCESS’'ARY VALVES are the smaller or less important testa- 
ceous plates, as distinguished from the principal or true valves. 
Ex. The small plates on the hinge of Pholas, fig. 55. a. 
ACEPHALOPH’ORA. BI. (a, without; Keane, cephale, head.) 
The third class of the type Malacozoaria, Bl. including all bi- 
valves, the animals of which have no distinct head. The Ace- 
phalophora are divided into the orders Palliobranchiata, 
Rudistes, Lammellibranchiata and Heterobranchiata, the last of 
which contains no testaceous mollusca. 
ACHATINA. Lam. (From Achates,an agate.) Fam. “‘Colimacea,”’ 
Lam. Limacinea, Bl. Potyrnemus, Montf. Descr. Shell, oval 
or oblong, sub-turrited, light, thin; aperture oval, pointed at the 
posterior extremity ; outer lip sharp; columella smooth, tortuous, 
truncated so as to form a notch at its union with the outer lip. 
Obs. It is from the latter circumstance that we are enabled to 
distinguish Achatine from Bulini, which, moreover, have a re- 
B 
