448 PEOF. W. A. HEEDMAN ON BEITISH TUIS^ICATA. 



The test is tough and leathery, rather tHu, wrinkled on the 

 outside, and smooth and glistening on the inside. 



The mantle isyery thick and muscular, and of a light grey colour. 



The branchial sac is large, with four large folds on each side. 

 There are from three to six bars between two folds, and eight or 

 nine on a fold. Meshes are either square or transversely elon- 

 gated, with four to eight straight stigmata (PI. XXXVl. fig. 11). 



The dorsal lamina is a plain membrane transversely ribbed. 



The tentacles are simple, about 30 in number and of different 

 sizes. 



The dorsal tubercle is large and somewhat cordate. It is 

 placed in a deep triangular peritubercular area ; one horn is 

 much turned in (PI. XXXVI. fig. 12). 



The stomach is longitudinally folded. 



The reproductive organs are in the form of numerous scattered 

 polycarps over the inner surface of the mantle. 



" Sttela etjstica (X.)." 



There has been much confusion in regard to this species in 

 our seas, and although various authors (from Porbes down to 

 myself) have named British specimens " Oynthia rustica" 

 '■^ Styela rustica^'' or " Folycmya rustica^'' I am now inclined to 

 think that none of these are referable to Linnseus's Ascidia 

 rustica, which is a Northern species probably not inhabiting the 

 British area at all. 



I think that what I at least have mistaken in the past for 

 small specimens of Styela rustica were really solitary individuals 

 of Polycarpa glomerata, which are sometimes found attached 

 to the " roots " of Laminaria ; and I first suspected that some- 

 thing was wrong when I found that, from the structure of the 

 reproductive organs, my supposed " rustica " was really a Poly- 

 carpa, not a Styela, and I pointed this circumstance out in my 

 Eeport on the L. M. B. C. Tunicata *. Then I put the matter 

 beyond doubt, so far as my own case was concerned, by dredging 

 large quantities of the true Styela rustica, of all sizes from a pea 

 up to 2 inches across, along with the closely allied form Styela 

 monoceros, to the north of the North Cape, Norway, in July 

 1891. The examination of this large series of specimens showed 

 (1) that rustica is a Styela, and (2) that it is quite distinct from 

 any form I have met with in British seas. Subsequently Canon 

 Norman kindly sent me his specimens of Styela rustica from 

 * Fauna of Liverpool Bay, vol. i. 1886. 



