512 



THE FUR SEALS OF THE PRIBILOF ISLANDS. 



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

 It woukl 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 ujion the main work in hand, 1 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 watchful 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, ."55 mm. Entire surface closely beset with short, 

 blunt, irregular tubercles. Color brown to yellowish 

 brown, a little darker at the ante- 

 rior end. (Eig. 1.) 



^. 



Test. — C o r i a c e o u s , almost 



homy, scarcely 1 mm. thick except- 

 ing through the tubercles. Dull 

 oi)a(iue white on cut surfaces; in- 

 ner surface, after being sei)arated 

 from tlie mantle, with a somewhat 

 pearly luster. Contains no vessels. 

 Mantle. — Well developed, con- 

 siderably thicker than test, com- 

 posed mostly of nuiscle fibers, most of which run lengthwise 

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

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

 Avhich is contained in irregular branched bodies (crystals? 

 excreted material?), and some diffused through the muscle 

 fibers themselves. 



Jiranchial 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 siiixple, about 24 in number, not of equal length, l»ut not 

 regularly alternating, a long and a short one; the circle close to the i)cripharyngeal 

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

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

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



]iranchial 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 



