CLASSIFICATION" OP THE TUNICATA. 64;1 



well-defined group, characterized amongst the £ree-s\vliuraing 

 forms by the absence of a tail and a notochord in the adult, and 

 by the occurrence of alternation of generations in the life-history. 

 Temporary colonies may be formed at one stage in the life- 

 history, but they never increase in size by gemmation from the 

 ascidiozooids, which eventually separate from one another. This, 

 along with the alternation of generations, distinguishes the 

 Thaliacea from the Ascidige Luciee Salpiformes), and the absence 

 of a tail and notochord separates them from the Larvacea. 



The Thaliacea may be divided into two groups, the Cyclomy- 

 aria and the Hemimyaria. 



Suborder I. CYCLOMYAEIA (Krohn), Uljanin, 1S84. 



Free-swimming pelagic forms which exhibit alternation of 

 generations in their life-history, but never form permanent 

 colonies. 



The body is cask-shaped, with the branchial and atrial apertures 

 at the opposite ends. The test is more or less well-developed. 



The mantle has its musculature in the form of circular bands 

 surrounding the body. 



The branchial sac is fairly large, occupying the anterior half 

 or more of the body. It has distinct walls, and the small slit- 

 like stigmata are usually present in its posterior part only. The 

 peribranchial cavity is mainly posterior to the branchial sac. 



The alimentary canal is placed close to the jDosterior end of the 

 branchial sac. 



Hermaphrodite reproductive organs are placed ventrally near 

 the intestine. 



The sexual generation in the life-history is always polymor- 

 phic. 



This suborder contains a single family only. 



Family DOLIOLID^, Xeferstein,18G2. 



Body free, more or less barrel-shaped ; branchial and atrial 

 apertures terminal and lobed. 



Test rather slightly developed. 



Mantle containing transverse muscle-bands, which form hoops 

 surrounding the body. 



Branchial sac well developed. Stigmata not numerous, gene- 

 rally placed far back. 



Dorsal lamina and tentacles absent. 



