REPORT ON THE ECHINOIDEA. 35 



able ; their small size, the gigantic size and often small number of their primary tubercles, 

 as weU as the peculiar shape of the primary radioles, all remind us of the early stages of 

 our present Cidaridae to a degi-ee which. can hardly be realised \\'ithout a direct comparison 

 of the figures of such Cidaridse as are given by Laube (Fauna d. Schichten v. St 

 Cassian, pis. viii.'' and ix.) with those of some young Cidaridse I have myself figured 

 (Revis. Echini, pi. ii.'' fig. 7) ; and the variety of form in the radioles found associated with 

 those in the St Cassian beds rivals the di.sproportions noticed in the spines of young 

 Echinidse and Cidaridse such as I have figured in the chapter on young Echini in the 

 Eevisiou (pi. ii.'^figs. 7-13 ; pi. v. fig. 9 ; pi. viii. fig. 16 ; pi. ix. ; pi. x.), and in the Embry- 

 ology of Echinoderms (Mem. Am. Acad., 1864). It is interesting in the description of the 

 variation in the shape of the spines which we find in Goniocidaris to see how early in 

 geological times this variation already existed as a character of the family, and has 

 persisted to the present day. 



The oldest species of Cidaris in the Trias were small species with smooth tubercles, 

 and the variety of radioles already apparent was considerable. Nearly all the types are 

 represented, but it is almost impossible to separate them, as there is a gradual passage 

 from one to the other. There is a great predominance of clavellate types, a great variety 

 of radioles with secondary spines, and a nearly total absence of the long cylindrical 

 radioles so characteristic of many of the Cretaceous, Tertiary, and recent species. This 

 variation in the spines and gradual transition recalls to us embryonic stages where 

 one and the same species passes rapidly from the state of embryonic species to the state 

 characteristic of the fully grown individuals. When we come to the Jurassic type of 

 radioles the varieties are less closely connected. They arrange themselves more easily 

 into two great types — the glandiarii and the aculei as Desor has named them, — 

 but we must remember that there are stdl transitional forms, or rather elongated 

 glandiarii with narrow necks approaching the aculei form of the others, and that 

 this formation is characterised by tlie far greater development of the elongated type 

 of radiole than in the preceding formation, their larger size corresponding to the 

 increase in the size of the test, and the immense development of species charac- 

 teristic of the Jura which have also mainly crenulated tubercles. This crenulation, 

 however, disappears again during the Cretaceous period, during which the Cidaridse 

 have smooth tubercles, but, as is the case also in recent species, do not on that 

 account carry smaller radioles. On the contrary, the latter are remarkable for their 

 great length, their greater variety in shape compared with those of the Jurassic period, 

 and more parti cidarly, as has been so well shown by Desor, for the first appearance of 

 the spreading into a corolla of the extremity of the spines so characteristic of some 

 Tertiary genera, and which seems to culminate at the present period in the cupuliform 

 spines of Goniocidaris. The glandiform radioles attain a degree of extreme development 

 unknown in the older formations, and they nearly disappear during the Tertiary period, 



