THE ASCIDIANS 23I 



regular in direction and length, between the larger ones, on the surface 

 of the infundibulte ; as a rule, the larger vessels only crossing from 

 one fold to the next. 



Stigmata long but irregular, rarely disposed in spiral form, so large 

 and numerous as to leave almost no expanse of branchial membrane 

 unperforated, its whole substance being composed of the narrower 

 bars between them. Considerable dark pigment along the edges of 

 the branchial folds and on the tentacles. 



Digestive apparatus. — Situated on left side, esophagus very short, 

 stomach relatively small ; intestinal loop narrow and long, extending 

 entirely across the posterior end of the animal : intestine of nearly 

 uniform diameter throughout its length ; anus somewhat trumpet- 

 shaped, adherent. 



Reproductive organs. — Situated on both sides of the body, ovary 

 on each side a single elongated cylindrical mass extending crosswise 

 of the animal ; in the single specimen at hand, testis apparently 

 wanting. 



This species is closely related to M. gregaria Lesson, but differs 

 from it in possessing the black, much-branched blood vessels in the 

 test, and also in the structure of the branchial sac. Herdman,^ who 

 has fully redescribed M. gregaria., states that the folds are narrow, 

 the internal longitudinal bars few, and that broad horizontal membranes 

 attached to the internal longitudinal bars run along the chief transverse 

 vessels. Moreover, the stigmata are rather small and are arranged in 

 spii'als. In all these particulars the two species differ distinctly. 



The single specimen was dredged at Sitka in about ten fathoms, on 

 June 15, 1899. 



RHIZOMOLGULA gen. nov. 



Pedunculate, the peduncle long and slender, bearing many 

 rootlets. Branchial sac with six folds on each side. Gonads 

 on the left side only, situated within the intestinal loop. 



RHIZOMOLGULA ARENARIA sp. nov. 



(PI. xxviii, figs. 10-192.) 



General characters. — Peduncle long and slender, giving off many 



filiform branches, or root hairs, which sei^ve as hold-fasts to anchor 



the animal to the sand. Body nearly spherical in form, though hav- 



1 Herdman, Report on the Tunicata of the Challenger Expedition, Part i, 

 1882. 



