BRITISH FOSSILS. 



Decade III. Plate VI. 



GALERITES (HOLECTYPUS) HEMISPH^RICUS. 



[Genus GALERITES. Lamarck. (Sub-kingdom Radiata. Class Echinoderraata. 

 Order Echinidse. Family Cassidulidse.) Body more or less hemispherical, always tumid ; 

 ambulacra simple, continuous, radiant ; mouth central, inferior ; anus inferior or sub- 

 marginal ; tubercles perforate.] 



[Sub-genus Holectypus. Body hemispheric, circular ; tubercles in regular series ; 

 inside without ribs.] 



Synonyms. Discoidea hemisphcerica^ Agassiz, Cat. Syst., p. 7. Desok, 

 IVIonog. des Galerites, p. 71, pi. 8, figs. 4-7 (1842). Holectypus hemi- 

 sphcBricus, Agassiz and Desor, Cat. Raisonne des Echinides, Ann. des 

 Sciences T^at., 3rd Series, vol. vii., p. 146. 



Vak. /3. Depressus. Discoidea rnarginalis, M'Coy, Ann. Nat. Hist., 

 2nd Series, vol. 11., p. 413 (1848). 



Var. y. Conicus, anus valde marginalis. Holectypus devauxianus 

 CoTTEAU, Etudes sur les Echinides Fossiles, p. 46, pi. 2, figs, 7-9 (1850). 



Diagnosis. G. (H^ testa tumidd, hcemisphcericd^ plus minusve depressd^ 

 margine rotundato ; ano marginali ; tuberculis in facie ventrali crebris, ad 

 orem semsim majoribus. 



The genus Holectypus has been founded by M. Desor for such 

 oolitic Galerites as have the aspect and regular arrangement of tubercles 

 distinguishing the genus Discoidea, but have not the internal ribs which 

 cause such deep indentations in the casts of specimens of the latter 

 group. They constitute a transition from the Discoidece to the typical 

 Galerites, and, according to my views, form a section on sub-genus of 

 the genus Galerites, more valuable on account of their palaeontological 

 merits and limited distribution in time (being in the main character- 

 istic of the oolitic period) than for the zoological importance of the 

 characters of their organization, which are rather transitional than dis- 

 tinctive. 



The type of the sub-genus Holectypus is the Galerites depressus, a 

 fossil very abundant in British oolites, and having wide vertical and 

 horizontal range. The species now figured is conspicuously distin- 

 guished from G. depressus by having a marginal instead of a vertical 

 anus, and the tubercles of its under surface very numerous and gradu- 



[iii. vi.] B 



