178 MR J. D. MACDONALD ON THE REPRESENTATIVE 



Table of Classification — continued, ...... Compound Tunicata. 



B. Palliovascular system intercommunicating. Genera. 



1. Excretory apertures opening directly into punctate, linear, or 

 reticulate cloaca. 



a. Biadominal (Polyclinian). 



1 . Systems single, isolated, or gregarious in whole relief, 



pendunculated (?), . . . . . Synoecium. 



2. Systems numerous, masses crusting. 



a. In half relief projecting above the surface, (?) Sidnyum. 

 h. Not projecting above the surface, . . Polychnoides. 



b. Thoracic (Botryllian). 



a. Cloacse punctate, ..... . Botryllus. 



b. CloacEe linear or reticulate, .... Botrylloides. 



SUB-CLASS II. 

 animals free locomotive. Pelagic Tunicata. 



Genera. 

 II. Branchial membrane, sac-like, tuith transverse slits in single longitudinal series, 

 strengthened by longitudinal non-ciliated rods, apertures terminal or sub- 

 terminal, ............ Pyrosoma. 



III. Respiring by an upper and a loiuer gill-band, connected with each other laterally 



a?id with the walls of the atrium ; having branchial slits, but no supporting 

 longitudinal rods. Apertures terminal, ....... Doliolum. 



IV. Respiring by a central and inferior gill-band with free borders, and transverse 



ciliated stripes, but without slits or rods. Apertures terminal or sub-terminal. 



1. Intestine short, and simply folded upon itself. 



A. Sexual zooids concatenated in chains. 



1. Ciliated stripes with pouch-like recesses at their outer ends, . Pegea. 



2. Ciliated stripes of gill-band, simple, ..... Salpa. 



B. Several zoids permanently united in circles, as in Pyrosoma, . . Pyrosomopsis. 



2. Intestine extended directly forwai'ds from a ccecum-like proventriculus. The 



anus, and with it the ejaculatory duct, opening near the branchial orifice, Orthocceta. 



(Salpa pinnata.) 

 V. Pharynx ciliated beloiv, without a distinct gill-band. Branchial slits reduced to 

 two ciliated openings on the sides of the rectum. Apertures approximated 

 hcemally, ........... Appendicularia. 



The lobing, and other particulars connected with the apertures, afford simple 

 and easily recognisable characters, which are often distinctive of genera ; but, as 

 the Table might be rendered too complex by their introduction, I have omitted 

 them. They may, however, be readily supplied by the student for his own con- 

 venience. I have drawn up the preceding scheme of classification chiefly with 

 the view of illustrating the principles set forth in the first part of the paper. My 

 own doubts I have expressed with a query (?), and even independent of these 



