(X'ULAK AN!) (JKMTAL I'l.ATKS. 



103 



relatively rare in the Cidaroida. The character of the apical disc in the I'alaeo/.oic ( ' idaridac 

 (Miocidaris) is unknown and would be most interesting to ascertain. 



Turning to the Centrechinoida, it is found that in this order the arrangement of the ocular 

 plates as regards insertness is much more definite and constant than in most of the < 'idaroidii. 

 Taking up the first suborder Aulodonta,' we find that in the Meso/oic Memicidaridae the lea-l- 

 ing character is for all the oculars to be exsert, as shown in the first two specie- li-ted in tin- 

 table. In Hemicidaris intermedia (169 specimens) the oculars arc exsert in X'.C , 'text-fig 

 but 13 specimens, 8%, are progressive variants with ocular I insert, and in five specimens, 3%, 

 the bivium is insert. In H. crenularis (58 specimens) 81 % have all oculars cxscrt, but 16% 

 are progressive variants with ocular I insert, and 2% progressive with oculars I, V insert, like 

 the typical character of the next higher species. One specimen is aberrant with ocular III 

 alone insert, a very rare variation seen in only two other sea-urchins (table, p. lf>4). 



In Hemicidaris luciensis typically, 56%, the bivium is insert (text-fig. 77) like tin- mo-t 

 progressive variants of H. intermedia. Seven specimens in 16, however, are arrested variant-. 

 two with all oculars exsert, the dominant character of the genus, and five with ocular I in-crt 

 (text-fig. 76), like the progressive variants of Hemicidaris crenularis and intermedia. Hemi- 

 cidaris langrunensis likewise has typically the bivium insert, 67%, as a species character. 

 but of 18 specimens, 11% have all the oculars exsert and 22% have ocular I only insert, as 

 arrested variants. In Hemidiadema stramonium (10 specimens) the oculars are typically all 

 exsert, 90%, but 10% are progressive with ocular I insert. In Asterocidarix minor (text-fig. 

 78), Goniopygus peltatus, and Glypticus hieroglyphicus (text-fig. 79) the oculars are strongly 

 exsert in all of the 134 specimens seen (table, p. 154). 



m m m 



TEXT-FIGS. 75-79.- Ocular plate arrangement in the Hemin.l:iri,l:i.-. 



75 Hemicidaris intermedia (Fleming). Coral Rag, Cain.-, Wilt*. K., K !,ind. Duun. .U mm. 



.dign y . Junu-e.B-h.ur Me, Diam. 22 mm. U. T. J. O,,., 7,v , , lllar , inMrt , 

 an arrested variant. ^ ^^ ^ y ^ fc ^^ 



?S. ^e^aris^nor Cotteau. Jura.io, Sollies, France. G. IJoehn, Co..., Fmbun. L . - - 

 79. Glypticus hieroglyphicus A g ^. Coral Rag, St. Pierre, Neuchatel. Eham. 19 mm. 

 all exsert. All figures X 4. 



The suborders of the Centrechinoida are now divisions ,Mi,,,-,l and discussed in the aection on cUficUo, d p. 183 



