320 Monograph of the Gaslerofodd. 



which are somewhat appressed above and veutricose below ; last volu- 

 tion somewhat flattened on the lower side ; aperture rounded, or 

 slightly transverse ; surface marked by numerous, strong, spiral carinse, 

 which frequently alternate with finer ones ; these are crossed by fine 

 strise, which, commencing at the top of the volution, pass obliquely 

 backward to the base, or into the umbilicus, sufl^ering no alteration of 

 their direction upon the carinse. 



This is a common form found at the quarries about Cincinnati, and 

 has a range very near or quite coextensive with the Cincinnati Group. 

 The shells differ very much in general appearance, and vary in size 

 from one fourth of an inch, or less, to more than an inch in height. 

 Prof. Meek characterized them as " varying from rhombic subglobose 

 to conoid-subtrochiform," which is sufficiently lucid without further 

 explanation. 



Prof. Meek figured a form in the Ohio Pala3ontology, for which he 

 proposed the name C hilix var. lata. It is so much depressed as to be 

 decidedly wider than high, and has along with the usual fine, regular, 

 revolving lines, and minute oblique strise of growth, strong, oblique, 

 rounded ridges, interrupted by a broad, shallow depression around the 

 middle of the upper slope of the body volution. This is the same 

 described by Mr. James, as C. Jluctuata, on page 152 of the April 

 number of this Journal. Its range commences more than 300 feet 

 above low water-mark, and extends to near the Upper Silurian, being 

 but little less in extent than the C. hilix, though it is comparatively 

 quite rare. 



I now propose the name Cydonema hilix var. conica, for the form 

 figured as a Cyclonema hilix, in the Ohio Paleontology, plate 13, figure 

 5gr, and characterize it as follows : shell conical, about one fifth longer 

 than greatest breadth ; volutions about five, flattened, usually rather 

 more convex on the lower than upper side ; suture ve^y shallow ; 

 aperture subquadrate and expanded belowj surface marked with 

 revolving lines, crossed by regular, finer, oblique lines, and occasion- 

 ally irregular, oblique ridges, giving it a beautiful cancellated appear- 

 ance. 



It will be readily observed that this is one of the extreme forms, 

 within the varying characters ascribed by Prof. Meek to this species. 

 But there is this reason at least for giving it the name of a variety : 

 it has never, to my knowledge, been found at Cincinnati, though Prof. 

 Meek had such information, as it seems, respecting the specimen he 

 figured. It is found at an elevation of about 600 feet above low water- 

 mark, thirty or forty miles east, west and north of Cincinnati, and has 

 a more restricted range than Prof. Meek's var. lata. 



