OCULAR AND CKMTAI. I'l.A'l I 97 



on the exterior from what they do on the interior of the test. The madreporite -how- -imilar 

 differential characters. On the exterior there are numerous line pores, hut on the interior only 

 one large madreporic pore as in the young, a primitive character common to tlie whole family. 

 Since typically in the Mediterranean form all oculars are insert, u .-penmen with any le mu-i 

 be considered an arrested variant. As such variants, 11',', have all ocular- e\-ert like tin- 

 dominant character in the West Indian form, 4% have V only insert, I ' , have V and I. the 

 bivium, 10% have V, I, IV, and 14% have V, I, IV, III insert. Of aberrant- there are five 

 specimens, 4%. Of these, one has V, IV only insert, two have V, I, III, and two have 

 V, IV, III insert. 



Cidaris affinis is an important species in these studies because it shows strongly the char- 

 acter of V, I, IV, III insert when four plates meet the periproct, instead of V, I, IV, II. The 

 same is probably true of a number of species in this order. Messrs. Agassiz and Clark (1907, 

 p. 40) in their Acanthocidaris hastigera give V, I, IV, III insert as the species character, but do 

 not say how many specimens showed it. It would be inter- 

 esting to know, as it is the only species of echinoid known in 

 which this is the character, as far as I am aware. 



Eucidaris metularia has typically all oculars exsert, but 

 in 39 specimens, two have V, I, IV insert as a progressive 

 variant. Eucidaris thouarsi has typically V, I, IV insert, but 

 the observations show a wide range of characters from all 

 exsert to all insert. This species is very close to Eucidaris 

 tribuloides of the West Indies. In both species oculars V, I, V 



IV are typically insert, but in thouarsi, arrested variants are 



J * J I i \T-KKI. til. Kiiriilnnxlnhuloidef 



common, progressive variants less frequent; while in tribuloides, ( i. ;llll;in k). Florida. I Mam. r, mm. 

 arrested variants are rare and progressive variants common, 



.... , t *!, individual. No genii til ami but frw 



indicating that thouarsi is the more primitive of the two 



madnponc ixinw, all orulara enert. 

 closely related species. Of Eucidaris tribuloides 849 specimens 



were studied, and they present most interesting characters. In the young of a few mm. in 

 diameter (text-fig. 61) all the oculars are strongly exsert and there are few madreporic p 

 The full number of oculars travels in very early. In the adult typically (58%), oculars 

 V, I, IV are insert (text-fig. 66). The variations of the adult as seen in the large > 

 studied are most interesting as the variants cover nearly the whole range of characters occur- 

 ring as species features in all regular Echini known from the Lower Carboniferous to the prc-mt 

 time. 1 The arrested variants are relatively rare, but progressive variants are common. Of 

 arrested variants, in 0.6% all oculars are exsert (text-fig. 62), as in the yom. B and the adult 



' The only known exceptions are Gymnechinus and Stnm.julwnlr,*!* giUi,*, in both of whirl, this arra in peculiarly 

 modified awl typically has an aberrant arran^m,,,. of oriilai* (..xt-figs. 154-157. ,,. 1 1.',, an.1 177 II 



