THE ASCIDIANS 255 



fold on the left side of the stomach triangular in form with very nar- 

 row base directed toward the posterior end of stomach, the apex reach- 

 ing nearly, though not quite, to the anterior end. 



Post-abdomen very dense and opaque ; gonads not recognized. 



Comparison of the points here noted with Herdman's description, 

 will show that the color of the colony, the distinct systems, and the 

 character of the stomach offer the chief difficulties to the identification 

 of the two forms as one species. 



Dredged at Sitka in about ten fathoms, June 15, 1899. A single 

 colony with two lobes. 



BOTRYLLUS MAGNUS sp. nov. 



(PI. XXX, figs. 33-37-) 



General characters of the colony. — Flat and incrusting, though 

 with a tendency to lobulation in some parts. Found on the under side 

 of rocks, to which it clings very closely. Irregular in outline, several 

 mm. (five or six) in diameter, 3 or 4 mm. thick, with pronounced 

 lobes here and there. Dusky purple in color, uniform in all parts, 

 and showing practically no variation from colony to colony. Systems 

 distinct, circular, regular. Five to eleven zooids in each system. 

 Common atrial orifices large, lobed, having as many lobes as zooids. 

 Each branchial orifice standing somewhat above the general surface. 

 The ectodermal vessels and ampullae in the test numerous ; the am- 

 pullae at tjie margins of the colony much longer than thick ; those in 

 other portions shorter. A mass of brown pigmented cells in the am- 

 pullae (p1. XXX, fig. 37). 



Zooids. — Large, 3.5 or more mm. long; 2.5 mm. broad. General 

 form that of a cylinder slightly curved with the convexity dorsal and 

 the ends nearly truncate. Full grown individuals rather opaque from 

 the considerable quantity of mesenchymatous material {J) and blood 

 in the mantle. Musculature of mantle exceedingly weak ; a, few scat- 

 tered fibers in the anterior end only, confined chiefly to the siphons. 



Branchial apparatus. — Branchial orifices distinct on surface of 

 colony; circular, not lobed, projecting slightly above the general level. 

 Six branchial tentacles projecting into the siphon in the living colonies. 

 Branchial siphon short and wide. Atrial siphon wide and fi'equently 

 of considerable length ; provided with a prominent ventral lip and 

 with a wide single-pointed doi'sal languet^ of very variable length, 

 wanting in young zooids (p1. xxx, figs. 35 and 36). 



Tentacles about sixteen, eight moderately long, and eight slightly 

 shorter alternating with these. Eleven to thirteen series of stigmata 



