GROWTH-STAGES OF "OROPHOCRINUS STELLIFORMIS" 75 



It follows from the preceding that such a description as that 

 given by Etheridge & Carpenter for O. stelUformis could not apply- 

 even to all the forms which they themselves labeled with that name. 

 Some of the necessary modifications will be gathered from what 

 has been said. There are other variations which may be mentioned. 



The deltoids are said to be constricted at one-third of their 

 length from the proximal end. In the large E 30091 the measure- 

 ments are 4.6/8.4 mm., i.e., more than one-half. In the medium- 

 sized E 30099 they are 1.8/3.8 mm., i.e., rather less than one-half. 

 In the smallest E 30106 they are 1.1/ 1.9 mm. 



The anal deltoid is said to have its distal margin rounded. This 

 seems to be the case in the two specimens from Burlington registered 

 E 841, as also in E 30096; but in most of the specimens the sutures 

 are straight, and, even when curved, nearly always meet in a 

 decided angle. 



The number of side-plates on each side of an ambulacrum is 

 given as fifty, on the authority of Meek & Worthen. It did not 

 reach this number in any of the specimens before Etheridge & 

 Carpenter. In E 1055 the total is thirty-five or less. In those 

 registered E 840, the total is forty or less, and in one case twenty 

 or less. In E 8172a, it is about twenty-five; and in E 8172Z), about 

 forty. In the very young E 30106 from White Ledge, the number 

 is about nine. From this it increases to fifty in E 30093, sixty in 

 E 30092, and something over sixty in E 30091. In E 842^, referred 

 to var. campanulatus by Etheridge & Carpenter, the number is 

 thirteen or fourteen, and was probably the same in 'E^?>2a. In all 

 individuals the number of side-plates to 3 mm. is nine or a fraction 

 more. 



The ornament, when preserved, as in E 30094, consists, on the 

 radials, of the usual growth-lines; these also occur on the upper 

 part of the basals, but on their lower part, where the basals form 

 a cylinder, the lines are coarse, irregular, and rugose. 



The cover-plates pass right up to the oral pole in E 30099, 

 apparently without fusion or enlargement. Since no one has ever 

 doubted that they could open on the ambulacra, there is no reason 

 why precisely similar plates should not have opened over the mouth. 

 Possibly these plates may have fused over the mouth in some 



