ASCIDIAXS COLLECTED IN PUG-ET SOUND. 263 



Mantle thin, but tough; musculature very regular, the 

 longitudinal bands forming almost a continuous sheet. 

 Both siphons distinctly 4-lobed. 



Branchial sac with 4 well-developed folds on each side. 

 With 8 to 9 internal longitudinal bars on a fold and about 

 10 in the interspace. Transverse vessels alternately 

 larger and smaller; there is also a narrow horizontal 

 membrane present dividing the meshes. Meshes trans- 

 versely elongated. 



Dorsal lamina a plain membrane. 



Tentacles about 32, closely placed, of different sizes. 



Dorsal tubercle prominent, rounded, with a narrow slit- 

 like opening forming a simple ovate figure, with one horn 

 running outwards (see fig. 2). 



Stomach elongated, and marked with a large number of 

 obliquely longitudinal folds. Intestine long, with 2 curves 

 (see fig. 3). 



Gonads. Two long narrow tubular ovaries on each side, 

 with groups of branched spermatic follicles arranged 

 around the posterior half of each ovary (fig. 3). There 

 are also many small transparent endocarps scattered over 

 the inner surface of the mantle and between the ovaries. 



Our specimens contained in the branchial sac several 

 specimens of the parasitic Copepod Doropygus pulex, 

 Thorell, both males and females. These were kindly 

 identified for me by Mr. I. C. Thompson, who says they 

 differ in no respect from examples of the same species 

 obtained in British seas. The specimens of Doropygus 

 are in their turn infested with a Vorticella. 



Fig. 1, on PI. XIII. , shows Styela gibbsii, natural 

 size ; fig. 2 is the dorsal tubercle enlarged ; fig. 3 the alimen- 

 tary canal and reproductive organs ; and fig. 4, a part of 

 the branchial sac from the inside, magnified. 



