THE ASCIDIANS 237 



The already rather large number of genera of the Molgulidcs^ sev- 

 ei*al of which are not very clearly defined and contain only a few 

 species, has made me very reluctant to add another one-species genus. 

 From this course, however, there seems to be no escape. Of the pre- 

 viously established genera, Etigyriopsis^ proposed by Roule in 1SS5, 

 and modified by Pizon in 1S9S, would receive this Alaskan species 

 with less forcing, perhaps, than would any other genus. This group, 

 regai'ded by Roule as a subgenus of Molgula^ was established for 

 species with a single sexual gland situated on the left side of the body, 

 outside and i?t fro7it of the intestinal loop. The last part of the 

 definition, it will be observed, would stand in the way of the admission 

 of the species under discussion. But Pizon has very I'ecently (1S9S) 

 concluded, after a consideration of the classification of the Molgulid(^ 

 based upon the examination of a considerable number of genera and 

 species, that Etigyriopsis should be regarded as a genus including all 

 species with gonads on the left side only ; and with curved stigmata, 

 inore or less regular, and more or less elongated, but not arranged in 

 the great infundibulse characteristic of Eugyra, The situation of the 

 gonads within or without the intestinal loop, he considers a matter not 

 of generic importance, and in this view I am disposed to coincide. 

 The gonads are so inconstant in this family, particularly as to position, 

 that the small difference here considered, at any rate when taken by 

 itself, seems insufficient to establish generic rank. If, however, it is 

 linked with the other characters, in which R. are7zaria differs from 

 Eugyriopsis^ viz. ; first, the possession of a pedvmcle, and second, the 

 presence of six folds in the branchial sac instead of seven, the coupling 

 of the two in the same genus is made obviously impossible. 



Another genus which has considerable claim on our species is Bos- 

 trichobranchiis Traustedt. Here the single gonad is situated on the 

 left side of the body and within the intestinal loop ; but the absence of 

 the peduncle and of true folds in the branchial sac, decides against the 

 admission of R. arejiaria to this genus. 



The only pedunculated genus of the family is Ascopera Herdman, 

 1882; but the peduncle here is an entirely different thing from that 

 of Rhizomolgula being nothing more than a somewhat produced pos- 

 terior end of the body. Furthermore, the infundibulcE in the bran- 

 chial sac are lacking, and the gonads are present on both sides of the 

 body, so that Rhizomolgula is far removed from this genus. 



The collection contains about thirty specimens all from Orca, Prince 

 William Sound, where they were taken on fishing lines by Dr. Coe 

 and Mr. Cole, on June 28, 1S99, ^^"^ about twenty fathoms. 



