THE " TRITON " TUNICATA. 95 



30, are over the " Wyville-Thomson " ridge, 7, 7-8, 8, 9, and 30 being towards 

 the NW. end, and 18, 20, 21, and 29 near the centre. 22 and 22-23 are 

 situated in the " cold area " near its southern end ; while 24, 28, and 31 are 

 in the " warm area " near the SE. end of the ridge. 3-4, 4, 4-5, and 5 are 

 between the island of Rona and the southern end of the ridge. 



Order I.— ASCIDIACEA. 



Family Cynthiid^e. 



Polycarpa pomaria, Savigny (PI. XVII. figs. 5 and 6). 



I have referred a small specimen from Station 3 to this widely distributed 

 and apparently highly variable species. I have not examined a sufficient 

 number of specimens to be able to say much as to the range of variation from 

 my own experience ; but from a comparison of the descriptions of other inves- 

 tigators, it is obvious that this is one of those interesting forms out of which it 

 is possible to make either one or half a dozen " species," according to the state 

 of one's critical faculties. Traustedt* describes it as Sty da pomaria, and gives 

 as synonymous Cynthia pomaria, Sav., C. coriacea, Alder, C. tuber osa, Macgill, 

 and Polycarpa varians, Heller ; while HELLERt suggests that Cynthia sulcatula 

 and C. granulata of Alder may also be varieties merely. 



There can be little doubt that Savigny's Cynthia polycarpa and C. pomaria 

 are merely varieties of the one species now known as Polycarpa pomaria, 

 Sav. ( = P. varians, Heller), and Cynthia tuberosa of Macgillivray is certainly 

 the same species ; while Alder's Cynthia sulcatula and C. granulata may 

 possibly be young individuals. But I cannot agree with Traustedt and 

 Heller in regarding Cynthia coriacea, Alder and Hancock, as another variety. 

 The description in Alder's Catalogue J states (1) that the ovaries are large and 

 white, and line the mantle with cylindrical convolutions, and (2) that the 

 branchial sac has about ten longitudinal folds, two important characters either 

 of which would be sufficient evidence to exclude the species from the genus 

 Polycarpa, while the second alone, if "about ten" may be taken as meaning 

 more than eight, cuts it off even from the sub-family Styelinse. 



The Triton specimen, which is a small one (2 cm. in length, 1*6 cm. dorso- 

 ventrally, and 12 cm. in thickness), was trawled at Station 3 (8th August 1882, 

 at the NW. end of the Wyville-Thomson ridge, and north of the " warm area," 

 bottom s. sh.) from 87 fathoms. Viewed from the side, it is rudely quadrate 



* Oversigt over defra Danmark og dets nordlige Bilande kjendte Ascidice Simplices. Vidensh. Meddel, 

 Nat. For., Kjbbenbavn, 1880, p. 415. 



f Vntersuchungen uber die Tunicatendes Adriatisclien und Mittelmeeres, Abth. iii. p. 19, Wien, 1877. 

 | Cat. Mar. Moll. Northumb. and Durbam, Trans. Tijnes. Nat. Field Club, vol. i. 1850. 



