512 



THE FUR SEALS OP THE PRIBILOF ISLANDS. 



/. 



with A. mutabile, Sars, from Hammerfest, than with any other species of the genus. 

 It would thus seem that at least half of the species might be regarded as character- 

 istically far northern; and the evidence at hand seems to justify the conclusion that 

 there exists a distinct Arctic Ascidian fauna. 



Before entering upon the main work in hand, I wish to express not only my 

 satisfaction at having the opportunity to make this contribution to the knowledge of 

 this group of animals, but also my pleasure at doing the work at the instance of one 

 so watphful and energetic as President Jordan ever is in all his capacities as a 

 promoter of learning. I also most gladly acknowledge the important assistance 



that has been rendered me in the work by one of my 

 advanced students, Miss Edith Byxbee. 



Dendrodoa tuberculata, new species. 



General characteristics. — Subcylindrical, about one- 

 third longer • than broad, quite regular in form, usually 

 attached by the posterior end, sometimes by one side. 

 Dimensions of a large specimen : Length, 53 mm. ; greatest 

 diameter, 35 mm. Entire surface closely beset with short, 

 blunt, irregular tubercles. Oolor brown to yellowish 

 brown, a little darker at the ante- 

 rior end. (Fig. 1.) ^ 



Test. — Coriaceous, almost > 



horny, scarcely 1 mm. thick except- 

 ing through the tubercles. Dull 

 opaque white on cut surfaces; in- 

 ner surface, after being separated 

 from the mantle, with a somewhat 

 pearly luster. Contains no vessels. 

 Mantle. — Well developed, con- 

 siderably thicker than test, com- 

 posed mostly of muscle fibers, most of which run lengthwise 

 of the animal; some "mesenchyme" cells among the muscle 

 fibers. An orange coloring matter in the mantle, some of 

 which is contained in irregular branched bodies (crystals'? 

 excreted material?), and some diffused through the muscle 

 fibers themselves. 



Branchial apparatus.— No projecting siphons, orifices 

 scarcely detectable, so completely are they hidden by the 

 tubercles of the test. Both situated at anterior end, not far 

 apart. Branchial tentacles simple, about 24 in number, not of equal length but not 

 regularly alternating, a long and a short one; the circle close to the peripharyngeal 

 band. Atrial tentacles present, numerous, short, and small. Dorsal tubercle con- 

 spicuous, biscuit-shaped, the horseshoe-shaped mouth of the hypoijhysis situated on 

 its surface, (Fig. 2 d. t.) 



Branchial sac, figs. 3 and 4, with four longitudinal folds on each side the pair 

 nearest the dorsal lamina somewhat larger than the others, each of these having about' 

 14 longitudinal vessels, while each of the others have about 10. Usually two or three 

 longitudinal vessels between each two folds. . Transverse vessels numerous averaging 



C3.0. 



