CONTENTS OF VOL. II. xh 
Page. 
Subdivision I. Cloak open. 
Tribe I. Valves closed by one adductor muscle. 
Pectenide. Ostreade, ‘ : . 504 
Tribe II. Shell closed by two adductor muscles. 
Avicularia. Meleagrina. Pinna. Arcade, { 505 
Subdivision IT. Cloak more or less closed, forming sy- 
phons. 
Tribe I. 
One syphon. Mytiluside. Uniode. Cardita. Vene- 
ricardia and Crassatella, : 505 
Tribe ITI. 
Cloak closed posteriorly, and anteriorly, forming three 
apertures. Tridacna and Hippopus, . - 506 
Tribe III. 
Anterior opening large. Chama. Cardium. Donax. 
Tellina, Venus. Mactra, : : 506 
Tribe IV. 
Anterior opening small. Mya. Solen. Pholas. Teredo, 507 
Section II. AcErHaLa Tunicara. 
Subdivision I. Interior tunic detached from the external 
one, and united only at the two orifices. 
Tribe I. 
Body permanently fixed to other bodies. 
A. Simple animals. 
1. Apertures furnished with four rays. Boltenia. Cy- 
nthia. Cesira. Styela. Pandocia, 509 
2, Apertures with indistinct rays of more than four. 
Clavelina. Pirena. Ciona, Phallusia : 511 
B. Compound animals, 
Branchial orifice radiated. 
a. Branchial and anal orifices, with six rays. 
Diazona. Polyzona.  Sigillina. ‘ Be 512 
