TUNICATA OF THE PRIBILOF ISLANDS. 



515 



not conspicuously corrugated. Color very light brown, uniform throughout. (Figs. 

 6 and 7.) 



Test. — Coriaceous, not hard, scarcely half a millimeter thick in thickest portions. 

 Mantle. — ^Not greatly developed ; somewhat thicker than the test; composed mostly 

 of longitudinal muscle fibers; does not readily separate from the test. 



Branchial apparatus. — No siphons; orifices obscurely 4 lobed, rather close 

 together, both situated at anterior end. Branchial tentacles simple, variable both in 

 number, size, and distribution. In one specimen about 20 i^res- 

 eut — a group of 4 long, large ones near the dorsal tubercle; 

 another group of about 10 large ones on the endostyle side, and 

 the other 6 smaller ones situated 3 on each side, comparatively 

 remote from one another. This arrangement of the tentacles 

 apparently typical for the species, though less perfectly carried 

 out in some specimens than in others. In some specimens not 

 above 14 tentacles present. The peripharyngeal band close to 

 the circle of branchial tentacles. Atrial tentacles present; un- 

 usually large; numerous. 



Dorsal tubercle conspicuous, biscuit shaped, the hypophysis 

 mouth horseshoe shaped, with out-turned limbs. 



Branchial sac with 4 longitudinal folds on the right side and 3 

 on the left; 1 or 2 internal longitudinal vessels between each two folds. The number 

 of vessels on the folds is as follows: Eight side, first fold, 10 vessels; second, 4; 

 third, 8; fourth, 4; left side, first fold, 11; second, 8; third, 4. (The folds are num- 

 bered from dorsal to ventral.) These numbers are quite constant. 



Distance between transverse vessels varies from 0.19 mm. to 0.50 mm. The ves- 

 sels are variable in size, but intermediate vessels — i.e., vessels crossing the stigmata — 



are rarely present. Dorsal lamina a plain 

 narrow membrane, situated somewhat to the 

 , left of the median dorsal line. 



"Endocarps" present, prominent, and ir- 

 regular in form, with a tendency to become 

 lobed. 



Digestive tract. — Situated on left side of 

 branchial sac, closely coiled, the posterior 

 half of the intestine running parallel, and in 

 contact with, the (i^sophagus and anterior 

 part of stomach. CEsoi)hagus not as long as 

 stomach. It issues from near the middle of 

 the dorsal side of branchial sac, the dorsal 

 lamina extending behind the opening and 

 passing to its left. Stomach considerably longer than broad, somewhat broadest at 

 oesophegeal end, not distinctly constricted off either from the oesophagus or from the 

 intestine; smooth walled on its external surface, but inner surface thrown into 

 numerous deep folds, causing it to resemble the psalterium of the ruminant 

 stomach. (Fig. 8.) 



Sexual organs. — Situated on right side of body only; ovary consisting of a basal 

 portion, extending autero-posteriorly along the ventral side of the animal, and 4 



B 



