636 CLASS X. 
Family IX. Balanotdea. Shell sessile, truncato-conical or 
tubular, calcareous, open at the apex; calcareous valves at the 
aperture. Animal conical, sometimes depressed. (Genus Balanus 
Brve.). 
Sea-Acorns, Sea-T'ulips. The pieces of shell, that form the calca- 
reous tube, shut upon each other with teeth. In some the base is 
closed by a calcareous plate, in which hollow tubes run from the 
middle to the margin, which communicate with other tubes in the 
length of the shell. Pot Testac. utriusque Sicilie, 1. Tab. Iv. figs. 
9,10. [Branching and inosculating ovarian tubes. Darwin Bala- 
nide, pp. 100, 101.] 
[To obviate the extreme confusion of the nomenclature, DARWIN 
proposes the following names for the external parts of Balanoids. 
What is visible externally of sessile cirripeds is composed of 
shell and operculum, the operculum being generally seated a little 
within the orifice of the shell. The shell consists of basis or support 
by which it is attached (membranous or shelly), and of compart- 
ments (8—4) occasionally all calcified together. The compartment 
as the end of the shell where the cirri are exserted is called carina, 
that opposite to it rostrum, those on the sides are the three lateral 
compartments, that next the carina the carino-lateral, that next the 
rostrum rostro-lateral, and the middle one simply the lateral com- 
partment. ‘These three are rarely present together. Each com- 
partment consists of a wall (paries) which always grows downwards 
and forms the basal margin, and is furnished on the two sides with 
ale or with radii, or with an ala on one side and a radius on the 
other. The radii, not always developed, on the upper part over- 
lap the ale, which usually extend about half-way down the 
compartment. The carina has always two alw. The cario- 
lateral and lateral compartments have always an ala on the rostral 
side and a radius on the carina]. The vostro-lateral (when present) 
always radi on both sides. The rostrum normally has ale on 
both sides, but very often, when fused with the rostro-lateral com- 
partments, it has radii on both sides. The operculum consists of a 
pair of scuta and a pair of terga, jomed to the sheath of the shell by 
the opercular membrane. On the internal surface of the scutwm 
there is almost always a pit for the attachment of the Adductor seu- 
torum muscle, and beneath the adductor ridge, often a pit for the 
depressor lateralis muscle. 
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