120 



BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



bearing the branchial aperture at the end. Atrial aperture but 

 slightly prominent, situated some distance back on the dorsal border. 

 Attachment by a large part of the left side. Test yellowish, very 

 smooth and shiny externally (much more so than in Phallusia de- 

 pressiuscula, just described), and of a glassy transparency and fairly 

 firm consistency. Apertures lobed, but in their contracted state the 

 lobes can not readily be counted. Length, 38 mm.; dorsoventral 

 diameter, 25 mm.; thickness from side to side, about 10 mm. 



Mantle thin and transparent, its musculature slight, comprising 

 slender radiating and circular bands on and near the tubes, and 

 scattered transverse bands on the right side in the ventral region, but 

 over most parts of the body no bands are noticeable. After removal 

 from the test a few minute bright red ocelli are visible around the 

 margin of the apertures. Eleven were counted about the branchial 



aperture; the number about the 

 atrial aperture was not determined. 

 Tentacles of three sizes arranged 

 with some approach to regularity; 

 a few additional fourth-order ten- 

 tacles are also present, and the 

 total number can hardly be less 

 than 50. 



Dorsal tubercle with an orifice 

 of irregular horseshoe form; its 

 open interval directed forward. 



Dorsal lamina nearly or quite 

 plain-edged in the anterior part; 

 but in the posterior part cleft into 

 numerous long narrow teeth, some of them dividing into two or 

 three slender points. 



Branchial sac in structure and appearance much like that of 

 Phallusia depressiuscula just described. (See fig. 74.) Transverse 

 vessels of two (in some parts three) orders fairly regularly arranged, 

 with occasional much larger vessels at intervals which are not always 

 in accord with the usual scheme of arrangement. Minute plications 

 of the sac well developed; they are less numerous than (in some 

 places only half as numerous as) the internal longitudinal vessels. 

 Internal longitudinal vessels well developed and complete, though 

 slender. They are separated by a varying number of stigmata 

 (usually from 9 to 13), the number being influenced by the develop- 

 ment and position of the minute plications already mentioned. At 

 the crossing of the transverse and internal longitudinal vessels, but 

 not at intermediate points, the latter vessels bear rather small curved 

 papillae. These are provided with a membrane along their concave 



Figs. 75, 76. — Phallusia apebta (Slui- 

 teu). 75, Left side ok body. X 1.25. 



76, DOBSAL TUBERCLE. X 7. 



