TUNICATA OF THE PRIRILOF ISLANDS. 



525 



37; 



llB: 



branchial siphon, with six quite regular, broad, low lobes. Atrial siphon with a 

 dorsal lauguet, but this ai)parently never of considerable length, usually broad and 

 blunt, sometimes, j)robably usually, three lobed, sometimes two lobed, and at least in 

 one instance observed, only one lobed. Contraction of branchial sac about equal 

 throughout its length, in no portion so great as to render the structure indistinguish- 

 able. Ganglion moderate in size, spherical, visible through the body wall. Tentacles 

 fairly well developed, about 24 in number, of unequal 

 length, somewhat more removed from base of siphon 

 than in the other species of the genus described in 

 this pajjer. About 10 series of rather small, short, 

 elliptical stigmata. A well- developed muscle band 

 in each iuterserial space of the sac. Dorsal lauguets 

 not conspicuous. 



Digestive tract. — Unusually small and contracted. 

 OEsophagus very short in proportion to its diameter, 

 at least as presented in all the specimens examined. 

 Stomach small and contracted, often apparently but 

 little greater in diameter than the rectal portion of 

 the intestine. Wall never with distinct longitudiual 

 folds, but never smooth. In some zooids it presents 

 merely thickened patches of irregular shape and un- 

 equal size, while in others there are distinct indications of areolation. In some indi- 

 viduals the areolae are elongated lengthwise of the organ, while in others their great- 

 est extent is crosswise of it, but this last condition may be the result of contraction. 

 (Figs. 21 A and 21 B.) 



Remaining portions of the tract without characteristic features. The constric- 

 tions of the intestine in the base of the loop irregular, but apparently never very 

 pronounced. 



Sexual organs. — Ovary immediately behind the intestinal loop in the peduncular 



portion of the post-abdomen. Ova large, contain- 

 ing much yolk; not numerous. Testis situated 

 behind the ovary and extending to the extreme 

 posterior end of the post-abdomen; composed of 

 many small lobes; vas deferens not conspicuous. 



Embryos developed to the completed tadpole 

 stage in the atrial chamber, this becoming much 

 distended by them. (Fig. 21). 



There are four colonies of this species in the 

 collection, all from St. Paul Island. 



Amaroucium pribilovense, new species. 



General character of the colony. — Massive, regu- 

 lar in outline, smooth surface, subglobular, very little or no indication of peduncu- 

 lation, though usually attached by small area only. Greatest diameter of largest 

 colony 5.5 cm., least diameter 3 cm. (Fig. 24.) 



Unyielding to the touch; dark gray with a slight olive tinge; considerable sand 

 adhering to and embedded in the surface. Zooids quite distinctly visible on the 

 surface. Testicular mass not large in quantity, the zooids being rather crowded, 



2¥ 



