54 The Ohio Journal of Science [Vol. XXI, No. 2, 



erately, but rather abruptly. From these zones it is evident that when 

 some of the larger plates were smaller, some of the still smaller plates 

 might have been absent altogether. In still earlier stages of growth only 

 those plates here called primary probably were present. If this view be 

 correct, then such species as Holocystites cylindricus and Holocystites 

 abnormis might be regarded as retaining their primitive characteristics 

 even in old age, and young specimens of species which in older age 

 resemble Holocystites alternatus might be expected to resemble Holo- 

 cystites cylindricus in their earlier stages of growth. 



8. Holocystites greenvillensis Foerste. 



Holocystites greenvillensis Foerste, Ohio Jour. Sci. 17, 1917, p. 203, PI. 9, Figs. 

 3 A, B, C; Plate 10, Fig. 8. 



This species, described from the Cedarville dolomite four and a half 

 miles east of Greenville, Ohio, is an excellent example of a small form of 

 Holocystites preserving its primitive characteristics, namely, about five 

 transverse rows of plates, each row consisting of about 8 plates, the 

 successive rows alternating with each other. 



9. Allocystites hammelli Miller. 



(Plate I, Figs. 13 A, B.) 



Allocystites hammelli Miller, N. Amer. Geol. Pal., 1889, p. p. 222, Fig. 242. 



Basal part, for a height of 5 mm., rapidly expanding from a width of 

 2.5 mm. to 6 mm.; bottom broken off; in place of a column there may 

 have been merely an attachment area as in Holocystites. This basal 

 part is followed by a circlet of 7 plates, the line of separation between 

 two of these being indistinct. The next circlet contains 8 plates of 

 larger size; in addition to this there are 3 pairs of accessory plates, 

 vertically arranged, separating adjacent plates from each other, and to 

 this is added another accessory area too poorly defined to be deciphered. 

 The following or third circlet also consists of 8 plates of larger size; in 

 addition there are accessory plates at 7 of the 8 intervening sutures; at 

 5 of these sutures the accessory plates are known definitely to be arranged 

 in pairs, one plate directly over the other; at the other two sutures the 

 same structure may exist but it is not decipherable. The following or 

 fourth circlet also consists of 8 plates of larger size; in addition there 

 appear to be pairs of accessory plates at 3 of the intervening sutures, 

 and single accessory plates at the lower ends of apparently 4 of the 

 remaining sutures. The anal aperture rests on the upper margin of two 

 of these plates of the fourth circlet and is enclosed, laterally at least, by 

 plates of the fifth circlet. The latter circlet consists of at least 7 plates, 

 the two in contact with the anal aperture being of exceptional width, the 

 remaining 5 being tall rather than wide. If there is a sixth circlet of 

 plates, its presence can not be detected in the type specimen. 



Surmounting the entire specimen, at least in its present condition, 

 is a protuberance 2 mm. in height, constricted at the base, with a 

 pentagonal outline at the top, with a width of 5.6 mm. between the 

 right anterior and left anterior angles, and a diameter of 4 mm. from 



