140 FOREIGN OOLITIC PSEUDODIADEMAS. 



tubercles, which at the base, and up to the equator, nearly equal in size the two rows of 

 primary tubercles ; this imparts a tetragrammous appearance to this species, which is lost, 

 however, in the upper part of the area, where there are only two rows of tubercles ; 

 ambulacra moderately wide, their tubercles nearly as large as those of the inter- 

 ambulacra ; pores unigeminal throughout ; apical disc small and ring-like, all the plates 

 covered with a fine granulation ; rows of small granules separate the areolas from each 

 other ; mouth opening large ; peristome not deeply notched. 



Dimensions. — Height, nine twentieths of an inch ; transverse diameter, one inch and 

 one twentieth of an inch. 



Formation. — Corallien de Bensancon, de Chatel-Censoir (Yonne). 



Collections. — Museum of Vienna (Collection Dudressier), Coll. M. Cotteau. Very 

 rare. 



Pseudodiadema ^equale, Agassiz. Syn. Diadema aquale, Agass., Echinod. Foss. 



Suisse, part ii, tab. 17, figs. 36 — 38. 



Test circular hemispherical, depressed above ; ambulacral rather smaller than the 

 inter-ambulacral tubercles; areolas confluent; four rows of small secondary tubercles, 

 which only extend to the equator ; upper part of the miliary zone naked ; mouth opening 

 moderately large ; peristome not deeply notched ; pores strictly unigeminal, falling into 

 triple oblique pairs near the mouth. This species very much resembles P. //emisp/iaricum, 

 but the smallness of the secondary tubercles, the shortness of the rows, and the nakedness 

 of the upper part of the miliary zone, distinguish it from that allied form. 



Dimensions. — Height, eleven twentieths of an inch ; transverse diameter, one inch 

 and two fifths. 



Formation. — Argovien des environs d'Arau. Kellovien des environs de Quingey. 



Collections. — Museum Bale, Coll. Zschokke, Marcou. Very rare. 



Pseudodiadema affine, Agassiz. Syn. Diadema affine, Agass., Echinod. Foss. Suisse, 



part ii, tab. 17, figs. 54 — 58. 



Test small, circular, depressed ; the secondary tubercles at the zonal sides of the 



