DESCRIPTIONS OF THE GENERA AND SPECIES. 



In the generic and specific descriptions, I have as far as possible followed the same 

 system as that employed in the case of the Simple and Compound Ascidians in the pre- 

 vious parts of the Report. The branchial aperture in all cases is regarded as indicating 

 the anterior end of the body, while the nervous system is dorsal, and the endostylc 

 ventral. 



I still make use of the classification given at the beginning of Part I. , with those 

 few additions which are rendered necessary by discoveries made since 1882. 



The class Tunicata is divided into three orders, the Ascidiacea, the Thaliacea, 

 and the Larvacea. 



Order I. ASCIDIACEA.^ 



This group includes fixed or free-swimming Simple or Compound Ascidians, which 

 in the adult are never provided with a tail, and have no trace of a notochord. The 

 free-swimming forms are colonies, and the Simple Ascidians are fixed. 



The test is permanent and well developed ; as a rule, it increases with the age of the 

 individual. 



The musculature of the mantle is in the form of an irregular network, there being 

 no regular circular bands. 



The branchial sac is large and well developed. Its walls are perforated by 

 numerous slits (the stigmata) opening into a single peribranchial cavity, which com- 

 municates with the exterior by the atrial aperture. 



The anus opens into tlie peribranchial cavity. 



Many of the forms reproduce by gemmation, and in most of them the sexually 

 produced embryo developes into a tailed larva. 



The order Ascidiacea is divided into three sections, — the Ascidl/e Simplices, the 

 AsciDiiE Co5iPOSiT.,E, and the AsciDi-s; Salpiformes. 



^ For the characters of orJer II. see page 36. and of order III. see page 96. 



