GEODIA AGASSIZII. 



133 



composing the sterraster protrude a short distance. The freely protruding 

 distal parts of these rays are usually circular or somewhat polygonal, four- to 

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

 hardly 1 p. 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 /i long and 1.3 n 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 [x long, and not regularly conical but 

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

 spinelets. 



DIMENSIONS OF STERRASTERS OF GEODIA AGASSIZII. 



Station 



2886 



2887 



2978 



3088 



3168 



4193 



82- 

 97 



4199 



4228 



4551 



AH 



stations 



4228 



Length 



of apparent- 

 ly full-grown 

 sterrastcrs, /( 



90- 



100 



97- 

 104 



90- 

 112 



110- 

 118 



100- 

 110 



85- 

 97 



95- 

 100 



95- 

 110 



107 



82- 

 118 



76- 

 100 



average of the 

 three longest, 



96 



102 



111 



118 



109 



91 



97 



9S 



103 . 55 



97 



Breadth 



of apparent- 

 ly full-grown 

 sterrastrrs, /( 



78- 

 83 



81- 

 90 



85- 

 100 



87- 

 95 



90- 

 96 



80- 

 83 



75- 

 8S 



so- 

 on 



83- 

 90 



7.5- 

 100 



70- 

 85 



average of the 

 three broad- 

 est, /( 



82 



88 



91 



91 



91 



82 



85 



88 



90 



88 . 56 



83 



Thick- 

 ness 



of apparent- 

 ly full-grown 

 sterraslers, /( 



58- 

 60 



65- 

 72 



74- 

 75 



78- 

 83 



6.5- 

 70 



63 - 

 70 



67- 

 70 



58- 

 61 



69- 

 73 



58- 

 83 



60- 

 70 



average of the 

 three thick- 

 est, 



59 



1 



71 



75 



81 



70 



66 



69 



61 



72 



6J . 22 



68 



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. 



