FOSSILS OF THE NIAGARA GROUP. 353 



gradually attenuate. Principal aperture subcentral ; arms originating 

 close to the aperture, and curving in a spiral direction over the 

 summit and along the sides to the point of greatest expansion, or 

 sometimes a little below. 



The specimens of this species are from one to three inches in length, 

 with a diameter in the greatest expansion of from less than half an inch 

 to an inch and a half 



The illustrations are of a large unsymmetrical specimen, and one of 

 symmetrical form somewhat smaller. 



Formation and Locality. — In the Hmestone at Racine, Wisconsin. 



GOMPHOCYSTITES CLAVUS, N. S. 

 PLATE XII a, FIG. 3. 



Body clavate, gradually expanding to the upper part which is elongate 

 ovate, nearly or quite symmetrical, summit regularly convex; prin- 

 cipal apei'ture at the apex, and essentially central. Arms originating 

 from one side of the central aperture, curving a little spirally down- 

 wards, and reaching below the apex a distance about equal to the 

 greatest diameter of the body. 



Below the expanded portion, the body becomes obtusely pentagonal, a 

 feature but obscurely shown in the cast ; base unknown. 



This species is very nearly symmetrical, and much more gradually 

 expanding from below to the greatest diameter, and less abruptly rounded 

 above ; while the arms have a more nearly vertical direction. 



It is possible that this may be only a modification in form of the G. 

 glans ; but among a considerable number of specimens of that species, I 

 have not observed gradations to this form ; and I therefore designate it 

 as a distinct species until it can be proved identical, or until its relations 

 with the preceding species can be more satisfactorily determined. 



Formation and Locality. — In the limestone at Racine, Wisconsin. 



GENUS HOLOCYSTITES, n. g. 



['oAof toius; CTffTof, Desico.] 



Body elongate, sub-cylindrical, elliptical or sub-ovate, composed of 

 numerous (six or more) ranges of comparatively large plates, or 

 of alternating series of large and small hexagonal or polygonal 



Cab. Nat. 45 



