102 
PALEONTOLOGY OF NEW YORK. 
order, but as a rule they are arranged in lines corresponding to the arching 
costas over which the callus lies. This is especially marked in figure 8, plate 
24. Rare examples are seen where the callus scarcely extends beyond the 
thickened margin at the edge of the aperture, while the pustules are already 
implanted upon the arching costas, and the spaces between them are gradually 
becoming undefined or obsolete. The pustules are often elongate, extending 
across two or more of the costas, as seen in figure 7, plate 24. These phases in 
the extension of the callus are shown in figures 27-29 of jslate 22, and in figures 
6—8 of plate 24. In a single longitudinal section the thickened columellar 
lip is shown, as in figure 30 of plate 22, and more extremely on plate 26. 
In its general expanded form this species resembles the B. Leda and B. Lyra , 
hut differs in the external markings. It has also the same general form as 
B. rudis of the Hamilton group, and B. trilirata of the Chemung group, but in 
the former the strong distant costas with distinct revolving strise or ridges are 
marked characters; while the tricarinate aspect of the other, together with 
the revolving strias are distinguishing features. In its arching costae it closely 
resembles the B. Newberryi; but in that species the volution is more depressed 
on the back, with the callus of the columellar lip smooth, and extending 
almost directly across the volution. 
Nearly all the specimens examined are more strongly striate on the back of 
the volution, near the expansion, than the one figured in the Geological Report 
of the Fourth District; but in other respects there is no important difference. 
In the prevailing forms of this species the aperture measures, in the 
transverse diameter, from one inch and five-eighths to one inch and six-eighths, 
and in the longitudinal direction about one inch and a quarter. Larger 
specimens have a transverse diameter of aperture of two and a quarter to two 
and a half inches, with a dorso-ventral diameter of about two to two and a 
half inches. 
Formations and localities. In the coarse shales of the Hamilton group in 
Schoharie county; in Otsego, Onondaga and Chenango counties; on the shores 
of Skaneateles, Cayuga, Seneca and Canandaigua lakes, and in the ravines 
entering those lakes; more rarely at York in Livingston county; and in the soft 
