CLASSinCATION OF THE TUNICATA. 625 



SiDNTUM, Savigny, 1816. 



Colony massive, or formed of a number of lobes, one corre- 

 sponding to eacb. system. 



Systems compound. 



Ascidiozooids elongated and distinctly divided into regions. 

 Branchial aperture 6-lobed ; atrial aperture not provided with a 

 languet. 



Test gelatinous. 



Branchial sac well developed. 



Alimentary canal forming a narrow loop. StomacL-wall areo- 

 lated or irregularly thickened. 



FostaMomen long, and separated from tlie abdomen by a con- 

 striction. 



This contains two species : — 



(Colony a globular mass, with broad rounded upper surface. 

 S. 2>cdlidum, Herdm. (A. Arct.) 

 Colony lobed, each system forming a truncated cone. 

 S. turbinaium, Sav. (N.W. Eur.) 



MoECHELLiTJM, Giard, 1872. 



Colony massive, sessile, or pedunculated. 



Systems compound, irregular, and usually inconspicuous. 



Ascidiozooids elongated, but not distinctly divided into regions. 

 Branchial aperture 6-lobed. 



Test gelatinous or cartilaginous. 



Branchial sac large and well developed. 



Alimentary canal usually large. Wall of stomach areolated 

 or irregularly thickened. 



Postahdomen large, but not distinctly separated from the 

 abdomen. 



This contains two species : — 



/ Colony pedunculated M. argus, M.-Edw. (N.W. Eur.) 



\ Colony sessile M. Giardi,'K&vdim. (A. Arct.) 



MoECHELLioiDES *, Serdman, 1885. 



Colony massive, sessile. 

 Systems compound, inconspicuous, 



Ascidiozooids elongated, but not distinctly divided into regions. 

 Branchial aperture 8-iobed ; atrial aperture anterior. 



* This section is very closely related to the next, Parascidia. 



