200 PALAEONTOLOGY OF NEW YORK. 



as great as the 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 strise 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 strise 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 stria) being more obvious than the concentric ones ; while in the 

 former species the longitudinal stria? are much finer and usually invisible, 

 except under a good magnifier. 



In its form and characteristic markings it resembles the //. solitarius of 

 Bakk\m)E (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 

 Bofume, vol. iii). 



Formation and locality. In the Hamilton group near Norton's Landing, on the 

 east side of Cayuga lake, N. Y. 



