GEODIA ACANTHTYIASTRA. 



193 



regularly distributed rays arise radially. The "rays are cylindrical or, more 

 rarely, conical, truncate, without the centrum 1-2 /i long, and 0.3-0.6, rarely up to 

 0.8 [i thick. Their distal part is covered with minute spines. These may either 

 all be so small as merely to render the ray rough in appearance, or some of them, 

 which usually form a verticil at or just below the end of the ray, may be larger 

 and clearly distinguishable as spines. Sometimes the ray appears terminally 

 thickened. Such asters have a somewhat acanthtyl appearance and may, if 

 large, be considered as transitional to the acanthtylasters described above. 

 The total diameter of the small strongylosphaerasters is 4.3 6.1 /«, usually 5-6 [x. 



The large strongylosphaeraster found in a centrifugal spicule-preparation, 

 which is probably a foreign spicule, has seventeen conic, truncate rays, at the 

 base 5 /< thick. The centrum is 13 n, the whole aster 23 ^< in diameter. The con- 

 vex terminal faces of the rays are densely covered with small spines. All the 

 other parts of the aster are smooth. 



The stermsters (Plate 45, figs. 28a, 39b; Plate 46, figs. 8, 9, 14-19) are 

 flattened ellipsoids, 65-76 ft long, 55-68 /t broad, and 42-46 /t thick. The average 

 proportion of length to breadth to thickness is 100 : 85 : 64. 



In young sterrasters of a certain developmental stage, in which the rays are 

 still terminally rounded, from two to five small rudiments of spines, standing 

 close together, arise from the summit of each ray. In the adult sterrasters the 

 protruding rays away from the umbilicus are 2.5-3 ft thick and bear terminal 

 verticils of usually five or six lateral spines, which are about 1.5 fi long and 

 remarkably stout. The transverse sections of the rays surrounding the umbilicus 

 are only slightly elongated in a direction radial to the umbilicus, and measure 

 about 3 by 4.5 /<. These rays usually bear from six to eight spines. The spines 

 directed towards the umbilicus are considerably larger than the others. 



The surface of the umbilical pit is uneven and often covered with numerous 

 conspicuous protuberances (Plate 46, fig. 19). 



The five specimens of this species were caught with the tangles at Station 

 2829 on May 1, 1888, off Lower California, in 22° 52' N., 109° 55' W.; depth 56 

 m. (31 f.); they grew on a rocky bottom; the bottom temperature was 23.4° 

 (74.1° F.). They were labeled F. C. 1342. 



The cribriporal nature of the afferents and efferents and the character of the 

 skeleton show that these sponges belong to Geodia. The spiculation differs 

 from all the other species of this genus as well as from those of Sidonops to 

 such an extent that a new species had to be established for it. 



