58 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. XXXIII. 



Stone camiL — Hith(>rt() the small, delicate stone canal has been 

 overlooked. It is single, straight, or convoluted, embedded in the 

 dorsal mesentery until near the madreporite, which projects free 

 in the coelom generall}' to the right, but in one case to the left of the 

 mesentery. The madreporite is kidney-shaped (fig. 11a), and consists 

 of two leaves or valves with thickened edges as if a round, thick- 

 lipped disk attached at the center to the stone canal had been once 

 folded, so that the opposite edges lie near together, forming the distal 

 portion of the structure. (Fig. llJ.) In the fifteen specimens exam- 

 ined one stone canal had its terminal part bifid for a short distance^ 

 each branch bearing a head of normal size; another had, besides the 

 usual madreporite, two small subsidiary heads, sessile upon the main 

 tube, a short distance from the distal end. Average length of the 

 stalk o mm.; of the head 0.8 mm. After treatment with potash it is 



found that at the junction 

 of the madreporite with 

 the stone canal the cal- 

 careous network is com- 

 paratively coarse and 

 open, but proceeding 

 toward the peripher}^ the 

 calcareous threads become 

 finer and the meshes 

 smaller, until in the thick- 

 ened rim they are de- 

 cidedly finer, densely 

 crowded, and clearly 

 marked off from the cen- 

 tral part of the disk. 

 Gonads. — In two tufts of simple tubules, one either side of the 

 dorsal mesentery. 



Respir<(to7'y trees.— Tl^fo, each with small branch given off near the 

 cloacal origin. The main stems are in the right and left dorsal inter- 

 radii, reaching nearly to the anterior end of the body, the right being 

 slightly longer. The branches lie in the right and left ventral inter- 

 radii, extending to about the middle of the body. 



Retractor 7iiuscles. — Strongly developed. In comparison the longi- 

 tudinal bands are weak. 



Ilahitat. — Massachusetts (Stimpson 1851, Verrill 1866). Cape 

 Breton Island, Nova Scotia (Whiteaves 1901). Labrador (Verrill 

 1866, Packard 1867). West Greenland to lat. 69° N. (Liitken 1857, 

 Norman 1876, Ludwig 1883). Assistance Bay, lat. 74° N., North 

 American Polar Sea to lat. 75° N., long. 95° W. (Forbes 1852, Dun- 

 can and Sladen 1881). Waigatsch Island, lat. 73° N. Kara Sea to 

 long. 64° E. (Stuxberg 1879, 1886). Plover Bay, Bering Sea (Lud- 



Fig. 11. — CucuMARiA calcigera. Stone i anal and mad 

 REPOKITE. a, Side view; h, distal view, (x 27.) 



