108 Cincinnati Society of Natural History. 



body may be said to be covered b}- four rauges of plates, with the ex- 

 ception of some irregular plates, which ma}' be found at the base, and 

 those surrounding the mouth, and those within the area surrounded by 

 the arm bases. 



The plates are generall_y pentagonal or hexagonal, but on the ante- 

 rior side the}^ do not come regularly together, in each range, and a 

 plate in the second range abuts against three plates in the third range, 

 instead of two, which produces, at this place, heptagon al plates. 



The only arm known rested upon two plates, supported by a third, 

 as shown by the base. The mouth and ambulacral orifice unknown. 

 All the plates are perforated by numerous elongated pores. 



This species was collected by Prof. A. G. Wetherby, in the lower 

 part of the Niagara Group, in Riple}' county, Indiana. The specimen 

 illustrated belongs to his collection. 



HoLOCYSTITES DYERI, n. Sp. 

 Plate X., fig. 3, view of the right side. 

 Bod}^ very large, and somewhat obovate, in form. It is covered by 

 about twelve or thirteen irregularly disposed ranges of plates. 



The first range, above the basal plates, consists of fifteen plates. The 

 second range has one or two more. The number increases in the third, 

 fourth, fifth, sixth and seventh ranges, though the plates are so irregu- 

 larlj' disposed that it is hardly proper to speak of them as ranges. In 

 the most ventricose part of the body, a I'ange, if I'egularly disposed, 

 would consist of about twenty-five plates. The plates are of unequal 

 size, usually hexagonal or pentag-onal, but sometimes heptagonal or 

 octagonal. They are more or less convex and highly poriferous. The 

 pores are elongated upon the outer surface, and distributed without 

 apparent order or arrangement. 



The summit of our specimens is so much injured, that it shows only 

 one of the arm bases, and consequently we can not define the apertures. 

 The species, however, is readily distinguished by its large size and 

 obovate form. 



The specimen has a length of three inches; diameter at the base, 



67-lOOtIis inch; diameter of the most ventricose part, 2 33 lOOths inches. 



The specimen described was found by C. B. Dyer, Esq., in whose 



honor it is named, in the lower part of the Niagara Group, in Ripley 



county, Indiana. 



rioLOCYSTITES VENTRICOSUS, U. Sp. 

 Phite X., fig. 4, view of left side of ventricose part. 

 This species is founded upon a single specimen, which is broken off 



