CIDARID^. 3 



larger and longer than nsnal, and the transition into tridentate pedicellaria) 

 can be traced step by step through a series of such intermediate forms. 

 More commonly a series may be found in which, by a gradual reduction in 

 size, the large globiferous intergrade with the small globiferous pediceUarioD. 

 The small globiferous pedicellaria3 are very similar to the large ones in 

 all essentials of structure, but the valves are more slender and the stalk 

 is much longer, and rarely, if ever has a limb. Often the valves differ in 

 some way very clearly from those of the large globiferous pedicellariae of 

 the same individual ; thus, if the latter have an " end-tooth " most of the 

 small ones may lack it, or vice versa. But they vary greatly, and in the 

 same individual may be found small pedicellarice the valves of which have 

 no end-tooth, and others in which it is conspicuous. And in some species, 

 moreover, the small globiferous pedicellarioe are just like the large ones 

 and intergrade with them completely. The valves of the small ones range 

 from .15 mm. upwards in length, while the stalk is often two or three times 

 as much and in some cases is five or six times as long as the valves. Small 

 globiferous pedicellariae may occur anywhere on the test except within the 

 areolae and the poriferous zones. They are particularly abundant on 

 the actinostome and on the actinal part of the ambulacra, but they may 

 be equally common on the abactinal system. Those with the shortest 

 stalks occur on the ambulacra, while those with the longest stalks are found 

 among the secondary spines of the scrobicular circles. They are never 

 entirely wanting except in the genus Porocidaris, where they are replaced 

 by very small tridentates. 



GONIOCIDARIDiE Haeck. 



CiDARis Klein. 

 Cidaris tribuloides Agass. 



Cidarites tribuloides Lamarck, 1816, Anim. s. Vert. Ill, p. 56. 

 Cidaris tribuloides Agassiz, 1835, Prodrome, p. 188. 



Plate 2, figs. 1-4, 



All three kinds of pedicellarice are present in most individuals, but 

 occasionally the tridentate are wholly wanting, and now and then only two 

 or three large globiferous ones will be found, even on large specimens. 



The large globiferous pedicellarite (PI. 2, fig. l) have the opening large, 

 terminal, with a well-developed lip and the margins conspicuously toothed. 



