176 MR J. D. MACDONALD ON THE REPRESENTATIVE 



social HDd compound groups. I hope, therefore, that this will be sufficient 

 apology, without complicating the table by continual reference to authority. 



CLASS TUNICATA. 



Marine molluscoid animals, fixed or free, invested by an outer coat or tunic 

 of variable consistency, and communicating with the exterior by an inhalent and 

 an exhalent orifice for respiratory currents, conveying also the materials used as 

 food ; having a ciliated and variously modified pharynx adapted for respiration, 

 and an atrial chamber for the discharge of the respired water and excretions, 

 a reversible circulation, sexes combined, and the power also of developing by 

 gemmation, which property pre-eminently distinguishes them from the mollusca 

 proper. 



SUB-CLASS I. 



ANIMALS FIXED OR STATIONARY. 



I. Branchial membrane closely adherent, or more or less perfectly sac-like, simply areolated, or 

 distinctly retiform ; the meshes disposed in many transverse series without non-ciliated siip' 

 porting bars. 



1 . GemmaB springing directly from the parent with a temporary bond ~j Simple 

 of union, ........... J Tunicata. 



A. Branchial membrane adherent, not forming a distinct sac. Ten- 1 Genera. 



taenia, o. Branchial folds transverse, ..... J Pelonaia. 



B. Branchial membrane more or less perfectly sac-like. 



1. Tentacula o, . . . . . . . . • (') Chelyosoma. 



2. Tentacula simple, liver rudimentary, animal sessile (erect or re- 



cumbent). 



a. Bi'anchial folds, o, ..... . Asddium. 



b. Branchial folds longitudinal. 



1. Branchial aperture higher than the cloaca], . Cynthia. 



2. Apertures on the same plane. 



a. Protected by a D-shaped apercular fold of the 



test common to both, .... Peroides. 



b. Simple or naked. 



1 . Ovary and testis on right side, . . Pandocia. 



2. Ovary and testis on the left side, . Dendrodoa. 



3. Tentacula compound. Branchial folds numerous, longitudinal ; 



liver well developed. 



a. Sessile (erect), apertures on the same plane, . . Ceesira and 



Molgula ? 



b. Pedunculated (pendulous) cloacal opening, the higher or 



subterminal, ....... Boltonia and 



Cystingea. 



