158 



MEDITERRANEAN PROVINCE. 



provinces ; those of our own Celtic coasts are some- 

 what numerous, but they are forms which, for 

 the most part, do not occur very readily, whilst the 

 more common ones, such as Ascidia intestinalis and 

 A. canina, as they are usually seen attached to the 

 roots of weeds thrown upon the beach, are but little 

 attractive. 



The geographical distribution of this class has 

 not yet been worked out. Certain genera of simple 

 Ascidians, such as Molgula, Peloncea, Boltonia, and 

 that very remarkable one, Chelyosoma, where the 

 leathery skin is thickened into tortoise-like plates, 

 seem to have a decided northern tendency. Molgula 

 and Peloncea are represented in our fauna, and our 

 Ascidians as a whole have a northern distribution. 



Some forms of this class have evidently a wide 

 range ; of our British species, Amouroucium argus, 

 Botryllus polycyclus, Ascidia mentula, and A. arach- 

 noidea are also Mediterranean. 



There is a large Ascidian found in the Adriatic, 

 in form somewhat like our common species, but 

 which becomes a beautiful object from the effect of 

 colour; in this — A. papillosa, the tough skin is 

 thickly overset w 7 ith disks of the brightest scarlet. 



The genera Euccelium and Diazona (a Medusa- 

 like Tunicary) are characteristically Lusitanian and 

 Mediterranean. The pelagic genus Salpa is repre- 

 sented here by more than a dozen species. Nu- 

 merically these free swimmers are more abundant 

 about the western than the eastern division. 



