MUSEUM OF COMPARATIVE ZOOLOGY. 27 



Preliminary Description of North Attlehorough Fossils. By N. S. Shaler 



and August F. Foerste. 



1. Obolella crassa, Hall, var. 



Plate I. Fig. 1. 



Shell oval or sub-circular, the beak projecting a little beyond the general 

 outline of the shell. The surface is marked by numerous concentric, lamellar 

 striee, and also by rather strong radiating striae. The latter, although usually 

 continuous throughout their Avhole length, frequently become more or less dis- 

 jointed and laterally displaced in passing across certain of the more marked 

 concentric striae. The radiating striae also vary at such points in their relative 

 prominence and distinctness. 



The interior of the shells differs considerably from that of typical specimens 

 of this species. The cast of the interior of the dorsal or anterior valve ex- 

 hibits two short triangular elevations at the beak, which represent the cardinal 

 area, and a depression between which corresponds to the cardinal tooth. On 

 either side are additional larger elevations, this pair representing the scars of 

 the cardinal muscles. Immediately above the second pair, the general surface 

 of the casts is strongly elevated, the elevation decreasing in distinctness to- 

 wards the margin. That part of this elevation which lies nearest to the hinge 

 margin is quite abrupt, and marks the position of the lateral muscular scars. 

 Along the median line of this elevation is a depression extending to above the 

 middle of the shell, the more or less distinct sides of which are known by 

 some writers as central muscular scars. 



The cast of the ventral valve shows a median elevation, narrow and promi- 

 nent, at the beak, which represents very likely a notch in this part of the 

 cardinal area of the original shell. On either side of this elevation are two 

 laterally directed notches, in front of which is an elevation representing cardi- 

 nal muscular scars, and the elevated portions immediately behind represent 

 lateral scars. No satisfactory central markings could be distinguished. Where 

 it seemed that these could be detected, closer examination has shown them to 

 be too faint for determination. 



Locality and position. — Stations Nos. 2 and 3, North Attleborough, Mass., 

 Cambrian, 160 specimens; also at Troy and Schodack Landing, N. Y. ; St. 

 Simon and Bic Harbor, Canada. 



2. OboleUa? 



Plate I. Fig. 8. 



Shell almost circular in outline, moderately convex, with no prominent 

 beak. The exterior surface is marked by concentric (exfoliated) striae of 



