﻿244 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 



[vol. 47 



Length of largest theca seen nearly 35 mm., while the average 

 length for a matured specimen is about 28 mm. 



Ambulacra prominent and wide, extending to near the base of the 

 theca. In some mature individuals the 5 primary ambulacra remain 

 simple: in others all bifurcate once, making 10 ambulacra near the 

 base of the theca ; in others still, all branch except the ray to the left 



23 



^ <% & & 23 



Fig. 35. — Analysis of Callocystites jewettii Hall, somewhat altered after Jaekel. 



of the anus and the one to the left of the lower pectinirhomb. In C. 

 canadensis further types of bifurcation occur, thus making it prob- 

 able that any 1 or 2 of the rays may remain simple while the others 

 divide. There is also no regularity in the period of branching, but 

 as a rule it takes place before half the size of the theca is attained. 

 On mature examples each simple or branched ambulacrum has on 

 one of the outer sides about 1 1 brachioles ; on the inner side of the 

 branches about 6 or 7. Brachioles very long and slender, from 11 

 to 12 mm. in length, and composed of about 30 to 32 pieces in each 

 range. Ambulacral grooves wide, not very deep, and covered by a 

 series of very minute quadrangular ambulacralia of which there are 

 in one range about 14 to 16 between each brachiole. 



Basal pectinirhomb with about 17 pores, the upper ones varying 

 between 12 and 15. Each rhomb usually is completely surrounded 

 by a high, thickened wall. The walls are most prominent on plates 

 5, 12, and 14. 



Madeporite yo -shaped and situated on the 2 parts of plate 23. 

 Hydropore immediately beneath the madreporite, very small, and 

 closed by a pyramid of 4 pieces. 



Anal area not prominent, the pyramid composed of 5 or 6 pieces, 

 and surrounded by a complete ring of 13 minute plates of variable 

 size. 



Column very stout, with thick joints near the theca, tapering 

 rapidly in the upper half and more slowly beneath. Total length 



