Eleventh Class. 
CONCHIFERA. 
Shell always bivalve, wholly or partly covering the Animal; sometimes free, sometimes 
Jfixed: the valves mostly joined at the margin by a hinge or ligament. The shell is 
sometimes enlarged by testaceous, accessory pieces, not belonging to the valves. 
Tus Class is divided into Two Orders, viz. Conchifera Bimusculosa, and Conchifera 
Unimusculosa. 
ORDER I._-CONCHIFERA BIMUSCULOSA. 
THE shell presents, in the interior, two separate and lateral muscular impressions: this 
order is divided into Four Sections, viz. C. crassipeda, C. tenuipeda, C. lamellipeda, 
and C. ambigua or the Chamacea. 
SECTION I.__-CONCHIFERA CRASSIPEDA. 
Shell gaping at the sides when shut. 
Tuis section contains Four Families —Tubicolaria, Pholadaria, Solenacea, and Myaria. 
TUBICOLARIA. —6 GENERA. 
AsPERGILLUM.—Sheath tubular, testaceous, gradually attenuating to the anterior end, 
which is open; the other extremity larger, and club-shaped; having two valves 
incrusted on one side of the club. The disk at the end of the club, convex, and 
perforated with sub-tubular holes, having a fissure in the centre. 
Plate II. Fig. 5. A. Javanum. (Serpula penis.—Linn.) [Mrs. Mawe’s Cabinet.] 
6. Front view of the disk. 
CLavaGELLA.—Sheath tubular, testaceous; the anterior end attenuated and open, the 
posterior club-shaped, ovate, and rather compressed with spinous tubes; one 
valve fixed in the side of the club, the other free in the tube. 
Plate II. Fig. 7 (a) C. aperta. (Sowerby.) [British Museum.] 
(b) The free valve. 
