NO. 1980. AHCtDIANS FROM NORTHEASTERN PACIFIC— RITTER. 499 



This species has considerable in common with P. ohliqua (Alder), 

 more seemingly than with any other. Indeed, in view of the fact 

 that the collection contains but a single specimen — too small a num- 

 ber on which to base a satisfactory description of a species — I have 

 tried to persuade myself that it might, provisionally at least, be con- 

 sidered as falling within the range of variation of ohliqua, particu- 

 larly as Hartmeyer has pointed out that ohliqua is a highly variable 

 species. However, the distinct 6 lobes of the branchial orifice, the 

 remoteness of the ganglion and gland from the hypophysis, and 

 the wide separation of the internal longitudinal vessels as com- 

 pared with the transverse vessels, not to speak of several less impor- 

 tant points, leaves no room for doubt about the distinctness of this 

 Alaskan species from ohliqua, its nearest of kin. 



Type-locality. — A single specimen, Alhatross 3315, lat. 54° 02' 40" N. ; 

 long. 166° 42' W. (north of Unalaska Island), 277 fathoms, gn.m.s., 

 August 15, 1890. 



Type.— C&t. No. 5685, U.S.N.M. 



PHALLUSIA ADHiERENS (Ritter). 



Ascidia adhxrens Ritter, 1901, p. 227, pi. 27, figs. 1-5. 

 Ascidiella prunum Hartmeyer, 1909a, p. 1401. 



Since Hartmeyer has considered P. odhserens a synonym for P. 

 prunum (JVIiiller), I have not only examined the specimens of the 

 collection now in hand with special care, but have reexamined the 

 original specimens from which adhserens was described and am forced 

 to conclude that the Alaskan animals possess features of considerable 

 and constant difference from P. prunum. Hartmeyer gives the ten- 

 tacle number for prunum as 40-50, this bemg the average of a large 

 number of specimens. The average number in adhxrens is un- 

 doubtedly much fewer. I agree with Hartmeyer that the number 

 of tentacles in this group is very difficult to determine with much 

 accuracy, is subject to much individual variation, and hence is not 

 of great value as a species character. Nevertheless, within wide 

 limits and when averages are taken, it is of some value. The average 

 for six specimens now before me I find to be 31, the maximum being 

 50 and the minimum 19. 



But the two most decisive features are in the branchial sac and the 

 alimentary tract. Van Name has recently pubhshed a drawing of 

 the branchial membrane of prunum.^ If this be compared with 

 figure 5, plate 27 (Ritter, 1901), showing the sac of adhxrens, it will 

 be seen that, while the areas bounded by the intersecting longitudinal 

 and transverse vessels in prunum are nearly square, in adhxrens at 

 least two areas between the transverse vessels are required to make 

 one between the longitudinal vessels. 



1 Van Name, 1912, pi. 66, fig. 129. 



