82 



BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



Body irregularly oblong, laterally compressed, especially in the 

 dorsal region, the tubes arising from the dorsal part of the body 

 far apart and pointing almost forward and backward respectively: 

 the branchial tube is the larger and longer of the two. Attachment 

 by the ventral region. Both apertures four-lobed. Test moderately 

 thick, tough and opaque, of a dirty whitish color. Surface of body 

 rough and uneven, and more or less overgrown with other organisms 

 except in the smallest specimens. Size of largest specimen, GO mm. 

 long and 38 mm. in dorso-ventral diameter. 



Mantle thin and somewhat transparent, with numerous regularly 

 disposed, rather broad, but not very compact muscle bands, which 



radiate from the bases of the 

 tubes and extend down on the 

 sides to the ventral region. On 

 the sides they cross each other, 

 forming an open network with 

 nearly square meshes. 



Tentacles of several sizes, the 

 large ones consisting of a stout 

 tapering stem bearing a wide 

 membrane and very short ta- 

 pering lateral branches, which 

 in turn bear a few lateral pro- 

 jections or more or less rudi- 

 mentary branches. The ten- 

 tacles of the first two orders 

 number together about a dozen ; 

 small tentacles are few. 



Dorsal tubercle large, irregu- 

 larly C-shaped with the open interval to the left (nearly forward in 

 the largest specimen) and the horns inrolled. 

 Dorsal lamina a plain-edged rather wide membrane. 

 Branchial sac with 9 folds on the left and 10 on the right side, 

 the last one incomplete or rudimentary, and the one next to it also 

 reduced. Transverse vessels of about four orders, the smallest cross- 

 ing the stigmata. They exhibit considerable irregularity in arrange- 

 ment in some parts of the sac, especially as far as the smaller vessels 

 are concerned. Five to eight stigmata generally intervene between 

 internal longitudinal vessels on the intervals between folds. Dis- 

 tribution of internal longitudinal vessels on the right side of body 

 in two specimens is about as follows: 



Smaller specimen: 



d. 4 (21) 4 (22) 4 (22) 5 (25) 5 (25) 6 (19) 5 (17) 4 (11) 2 (10) 2 (3) 1 v. 



Larger specimen: 



d. 4 (26) 5 (30) 6 (36) 6 (34) 5 (30) 5 (26) 5 (24) 5 (20) 4 (16) 3 (5) 1 v. 



if 



Figs. 30-32.— Microcosmus kxasperatus 

 Heller. 30, Left and right sides ob 1 

 body. X .75. 31, Tentacle, x 10. 

 32, Dorsal tubercles op two indi- 

 viduals. X 3.5. 



