GEODIA AGASSIZII. 



133 



composing the sterraster protrude a short distance. The freelj^ protruding 

 distal parts of these raj^s are usually circular or somewhat polygonal, four- to 

 seven-sided, in transverse section, 1.3-4 /t thick, regularly distributed, and 

 hardly 1 /z apart. They are truncate, and from the margin of their terminal 

 face a verticil of from four to seven, most frequently six, spines arises. These 

 spines extend either transversely, vertical to the axis of the ray, or, less fre- 

 quently, obliquely outward and a little upward. The spines of the rays remote 

 from the umbilical pit are stout, straight cones, about 1.7 /z long and 1.3 /i thick 

 at the base (Plate 31, figs. 1, 2, 6, 7; Plate 33, figs. 12, 13). Those of the 

 spines of the rays surrounding the umbilical pit, which extend towards the 

 umbilicus, are often larger, as much as 2.5 ju long, and not regularly conical but 

 irregular, their ends being broad and sometimes covered with small, secondary 

 spinelets. 



DIMENSIONS OF STERRASTERS OF GEODIA AGASSIZII. 



Besides these normal forms of full-grown sterrasters, which form the great 

 majority, some others with fewer and usually stouter protruding rays and more 

 numerous or larger and differently shaped spines, which I propose to name 

 sterroids (Plate 31, figs. 3, 4, 8-10; Plate 32, figs. 13-28, 33, 34, 36-39; Plate 

 33, figs. 9-11, 14), are met with. 



