Ri CONCHOLOGY. 75 
a mantle closed above, open below, and especially to the rear, 
where it forms sometimes a sort of tube furnished with tentacular 
cirri: a flabelliform abdominal appendage, and a very consider- 
able byssus ; mouth provided with double lips, beside two pairs of 
labial appendages ; a single large rétractile muscle apparent. 
Shell. Subcornate, fibrous, brittle, regular, equivalve, longi- 
tudinal, triangular, pointed anteriorly, in which direction is the 
summit, which is straight, wide, and frequently truncated poste- 
riorly ; hinge dorsal, longitudinal, linear, toothless ; ligarhent occu- 
pying nearly all the dorsal edge of the shell; a single and very 
wide muscular impression posteriorly ; a trace of the anterior in 
the summit. Inhabits the Mediterranean Sea. Fifteen species. 
Pinna rudis. Pinna flabelium. 
P. seminuda, P. angustina. 
P. nobilis. P. squamosa. 
P. marginata. P. muricata. 
P. pectinata. P, saccata. 
P, ingens. P. dolabrata. 
P, varicosa. P. vexillum. 
P, nigtina. 
FAMILY XVII. 
Mattracea. Five genera. 
1. Genus Crenatula. Pl. VIII. 
Animal. Unknown. 
Shell. Irregular, much flattened, subrhomboidal, subequivalve, 
gaping posteriorly ; summit anterior; hinge longitudinal, dorsal, 
toothless ; ligament submultiple, or inflated from place to place, 
and inserted in a series of round cavities corresponding with the 
dorsal edge ; muscular impression unique and subcentral. In- 
habits the Red Sea. Seven species. 
Crenatula modiolaris. Crenatula bicostalis. 
C. avicularis. C. viridis. 
C. nigrina. C. mytiloides. 
C. phasianoptera. 
