192 
the basal edge. Some are covered by a kind of hairy epidermis. 
Blainville says, that the animal has the body thick, of a somewhat 
variable form; abdomen provided with a pedunculated, compressed 
foot longitudinally divided ; mantle with a simple range of cirri, 
and a little elongated before ; the tentacula are very small and 
very slender. 
[Aeca staminea, pi. 36, fig. 2, and Akca lienosa, pi. 36, fig. 1, being 
fossil species, I have omitted the descriptions. — En.] 
V SiPHONARiA. — Shell oval or subovate, patelliform ; apex nearer 
one side and one end, curved in a direction opposite to an angle 
on the basal edge ; within, an indentation dividing the muscular 
impression and extending to the angle of the lateral edge. 
Ohs. Adanson was the first to detect the differences between a 
species of this genus, the S. mouretus, Bl., and Patella which it 
resembles in general form. He was succeeded by Blainville, but 
it is to Sowerby that we are indebted for the genus and name 
which are now adopted. Grray formed a genus for the Gadin of 
Adanson, which, however, is referred by other authors to the present 
group ; Adanson did not describe its animal ; but it is evident 
from his figure that the two sides of the shell are not symmetrical. 
It resembles Patella., but the shell is distinguished by an un- 
symmetrical angle on one side, (sometimes obsolete,) denoting the 
position beneath of the termination of a syphon or respiratory organ 
I of the animal of which the trace remains. On the outer surface, 
corresponding with this mark, is generally an elevation or rib, ex- 
tending from the summit to the edge, but it is sometimes obsolete. 
Blainville gives the following characters of the animal : body 
oval subdepressed ; head subdivided in two equal lobes ; tentacula 
and eyes indistinct ; margin of the mantle crenulated and extend- 
ing beyond a suborbicular foot as in the Patellas, branchial cavity 
transverse, open a little before the middle of the right side and 
provided in that part with a fieshy lobe, of a square form, situated 
in the sinus between the mantle and the foot ; retractor muscle of 
the foot, divided into two parts, of which the posterior is much the 
larger, arquated ; the other very small, before the branchial orifice. 
Several species are known, attaching themselves to rocks and 
other fixed bodies. 
SiPHONARiA ALTERNATA.-— altemataj noh. Jour. 
Acad. Nat. Sc. vol. 5, p. 215. 
