136 Transactions of the Canadian Institute. [vol. ix 



greatest degree of certainty is Telhyum coriaceum, the T. papillosum of 

 Gunner and the Ascidia papillosum of Linne. This may be taken as the 

 type of Tethyum. 



Heller has indicated the same species as the type of Cynthia Savigny. 

 Halocynthia Verrill and Lais Gistel were instituted to replace Tethyum. 

 All three are therefore absolutely synonymous with Tethyum. 



As defined above, this genus comprises a group of species, which 

 dififer from all other Tethyids in the position of their gonads. It in- 

 cludes T. pyriforme (Rathke), T. aurantium (Pallas), T. roretzii (Drasche), 

 T. hilgendorfii (Traustedt), T. igaboja (Oka)and probably a number of 

 others which have not yet been sufficiently described for one to be sure 

 as to their position. 



T. aurantium (Pallas). 



Syn — .Ascidia aurantium Pallas, Nov. Act. Ac. Petr., vol. II, p. 240. 

 Cynthia pyriformis Dall, Amer. J. Conch., vol. VII, p. 157. 

 alt. auct. (Pacific). 

 " superha et deani Ritter, Ann. N.Y. Ac, vol. XII, p. 

 590. 

 A very few specimens from various points — Departure Bay, Uclue- 

 let. Banks Island and between Cortez and Hernand Islands, in from 10 

 to 30 fathoms. 



T. pyriforme from North Europe and the Arctic Ocean has, accord- 

 ing to Hartmeyer (1903), 4 gonads on the left side and from 4 to 6 on the 

 right. 



All the Pacific specimens, that I have been able to examine, have 

 3 gonads on each side. They seem to be for that reason, quite distinct 

 from T. pyriforme. From Traustedt's account (Vid. Meddel. Kbhvn., 

 1885, p. 34), I conclude that his Corean specimens had 3 gonads on each 

 side. That would make the Asiatic and West American forms identical, 

 Pallas' name, being the first one given, is the valid one for this group. 



T. igaboja (Oka). 



Syn. — Halocynthia igaboja Oka, Ann. Zool. Jap., vol. VI, Pt. i, p. 45. 

 ? " okai Ritter, Univ. Cal. Publ. Zool., vol.IV, p. 11. 



A number of specimens from Departure Bay, Ucluelet, Lowe In- 

 let and Prince Rupert, in from 10 to 30 fathoms shelly or gravelly. 



These specimens are in accord with Oka's description and differ 

 from Ritter's only in regard to the inrolling of the horns of the dorsal 

 tubercle. The gonads are quite variable, there being from 2 to 16 on the 

 right side and from 5 to 14 on the left. 



