GEODINELLA ROBUSTA. 217 



Plate 4, fig. 13). These rays are cylindrical, 3 /< long and about as broad, and 

 rather uniformly distributed over the surface, their axes being 5 // apart. Those 

 portions of the surface of the central mass of the sterraster which lie between the 

 rays are more or less roughened. At the end each ray bears a verticil of stout, 

 conic, lateral spines, 1-2 pt long and broad, the axes of which are vertical to the 

 axis of the ray. The average number of the spines in a verticil is six ; but there 

 may be as few as one or two or as many as eight or ten. 



Among these ordinary sterrasters, forming, as stated, the great majority 

 in all the three varieties, a few sterroids occur, which are similar to these in shape 

 and size, but have different rays. Two kinds of sterroids can be distinguished. 



In the one, which is observed more frequently, the rays are, as in the normal 

 sterrasters, quite uniformly distributed and close together, but wholly or in 

 part much larger and crowned with a much greater number of spines. In these 

 sterroids (Plate 3, figs. 4, 6; Plate 4, figs. 14, 15) the rays attain a thickness 

 of 7-10 /x, the spine-verticils are composed of 15-20 spines, and the convex 

 apical ends of the rays also bear several, usually 4-8, spines equalhng in size 

 the verticil-spines (Plate 4, figs. 14, 15). In these sterroids the verticil-spines 

 are usually directed slightly downwards, the whole verticil appearing as the 

 serrated and somewhat recurved margin of a terminal, shield-like expansion of 

 the ray, from the distal face of which several spines arise. 



The other kind of sterroid (Plate 3, figs. 5, 8), which is very rare, consists 

 of a central mass of the usual ellipsoidal or a more spherical shape, from which 

 rather sparse and irregularly distributed rays arise. These rays are cylindro- 

 conical, 22-27 /x long, 11-17 p. thick at the base, and covered with numerous 

 small spines ; on the parts of the surface of the central mass free from rays such 

 spines also occur. On the rays the spines form extensive patches within which 

 they stand quite close together. On the central sphere they are for the most 

 part farther apart and irregularly scattered. Here and there well marked, 

 smooth, channel-like zones separate adjacent spine-patches. 



The four specimens of this species were obtained on the Pacific slope of 

 North America. One specimen of var. carolae was trawled at Station 4199 on 

 June 25, 1903, in Queen Charlotte Sound off Fort Rupert, Vancouver Island, 

 B. C; centre of Round Island S. 46° W., 11.5 km. (6.2 miles), drift S. 85° E.; 

 depth 124-196 m. (68-107 f.); it grew on a bottom of soft green mud and vol- 

 canic sand; the bottom temperature was 7.7° (45.9° F.). The specimen of var. 

 megaclada and one specimen of var. carolae were trawled at Station 4228 on July 

 7, 1903, in the vicinity of Naha Bay, Behm Canal, S. E. Alaska; Indian Point, N. 



