200 
PALAEONTOLOGY OF NEW YORK. 
as great as tlie vertical, the body being flabelliform, with the apex much 
elevated, the sloping sides concave, and limited by a distinct groove. 
Above this groove is a slight fold, separating it from the flattened 
triangular area, which is turned forward at an angle of more than forty 
degrees to the plane of the axis of the operculum, and marked in the 
centre by a distinct pit; the whole presenting much the aspect of the 
area of a spiriferoid brachiopod, with the foramen in the centre. (See 
plate 32 A.) 
Surface of the shell marked by fine concentric striae of growth, which are 
sometimes crowded into fascicles; and these are crossed by stronger, equal 
and continuous longitudinal striae. The body of the operculum is radi- 
atingly striated from the apex, and the area presents some indistinct 
ridges or folds; the concentric striae are not visible under an ordinary 
magnifier, but there are distant concentric folds parallel to the anterior 
margin, which are quite perceptible. 
Length of fossil in one specimen measured about twenty-one millimetres, 
and another one, when entire, has been considerably longer; width at the 
base from five to six millimetres. This species is readily distinguished from 
H. aclis by its proportionally more slender form, and in its continuous, strong, 
longitudinal striae being more obvious than the concentric ones ; while in the 
former species the longitudinal striae are much finer and usually invisible, 
except under a good magnifier. 
In its form and characteristic markings it resembles the H. solitarius of 
Barrande (plate 13, figs. 34 and 35), and it has nearly the size and proportions 
of that species. The geological relations of the two species are, however, 
quite different. Our species, in its surface-markings, may be compared with H. 
obvius of Barrande, as given in figures 1-4, plate 12 ( Syst. Sil. du centre de la 
Baht me, vol. iii). 
Formation and locality. In the Hamilton group near Norton’s Landing, on the 
east side of Cayuga lake, N. Y. 
