W. G. Van Name — Bermuda Ascidians. 355 



form are, when small, of rather similar ap])earance to those of this 

 species; but the somewhat stouter zooids, with much more numerous 

 and often much less regular plications in the stomach-wall ; the very 

 milky appearance of the test ; and the tendency to form wedge- 

 shaped or pedunculated colonies, would serve to distinguish the New 

 England species, even if it did not form massive colonies of vastly 

 greater bulk than this species ever attains. 



Family DIDEMNID^ Verrill, 1871. 



Colony incrusting, sometimes thick and massive, not peduncu- 

 lated. Test usually containing bladder-cells and often calcareous 

 spicules, which are generally of stellate form. Zooids arranged in 

 complex branching systems. 



Zooids of small size, divided into thorax and abdomen, often with 

 a muscular and vascular process extending out into the test from the 

 region of the peduncle connecting the two divisions of the body. 



Branchial aperture six-lobed ; atrial plain, or with a languet. 

 Three to six rows of stigmata. Dorsal lamina with languets. 



Stomach smooth-walled, externally at least. Intestinal loop 

 twisted. 



Reproductive organs on the left side of the abdomen, or more or 

 less ventral, or posterior. Testes few, often only one. Vas defer- 

 ens often spirally coiled about the testis before leaving it to follow 

 the intestine. There is no oviduct. 



Budding from the pyloric region (near the peduncle) ; thorax and 

 abdomen of the new zooid formed from separate buds. 



The genera Diplosoma, and Dlplosomoides, which are often 

 regarded as constituting a separate family, the Diplosomidte, are 

 here included in this family. 



Genus Didemnum Savigny, 1816. 



Colony generally rather thick and fleshy. Test containing blad- 

 der-cells and usually stellate calcareous spicules. 



Zouids with a strong muscular process extending into the test 

 from the ventral side of the peduncle connecting the thorax and 

 abdomen. Branchial orifice six-lobed, atrial plain, with no languet. 



Branchial sac with three rows of stigmata. 



Testis single, more or less conical in form. The vas deferens 

 makes a number of spiral turns about it before proceec\ing on its 



