494 PHILOSOPHY OF ZOOLOGY. 



the heart. There is an auricle on each side, receiving the 

 aerated blood from each of the gills. 



2d Tribe. 



Shell conical, simple, or slightly revolute at the apex. 



A. Cavity of the shell interrupted by a testaceous plate. 

 This division consists of three genera, each of which may 

 be regarded as the type of a family, although, for the pre- 

 sent, they are all included in one. 



Family, Crepididadce. The marine genera are, Crepi- 

 dula and Calyptrea, the latter including the Patella Chi- 

 nensis of British writers. In the former, the gills form a 

 transverse ridge on the roof of the cavity, consisting of fila- 

 ments extending beyond the margin. The eyes are at the 

 base of the tentacula. There is only one fluviatile genus, 

 termed Navicella. 



B. Cavity of the shell entire. 

 Family 1. Capulitside. Shell entire. 



This includes the genera Capulus (containing Patella, 

 Hungarica^ and Antiquata, of British writers) and Cari- 

 naria, represented by the Argonauta vitrea. In the Capu- 

 lus, the foot is complicated on its anterior margin. The 

 shell adheres to the animal by a circular muscle, leaving an 

 opening in front, for the issue of the head and entrance to 

 the branchial cavity. The gills form a single ridge across 

 the roof. The mouth is in the form of an extended pro- 

 boscis, with a deep groove above. The tentacula, which 

 are two in number, have the eyes at the external base. The 

 anus is on the right side of the branchial cavity. In the 

 Carinaria, the foot appears to be compressed, and formed 

 for swimming. The head is covered with a group of tu- 

 bercles. The mouth is furnished with a proboscis. Near 

 the middle of the body, the shell is attached. The surface 

 of the body above is closely covered with small tubercles* 



