110 PALEONTOLOGY OF THE EUEEKA DISTEICT. 



muscular scars. The posterior adductor scars (pa) are large, elongate-oval 

 in outline, and so situated that their anterior portions cross a line drawn 

 through the transverse center of the valve, while the posterior ends point 

 back to their path of advance; they are separated by the track of advance 

 of the anterior adductor scars (aa), which are seen just in advance of 

 them as very small, slightly impressed oval spaces. The area of the ad- 

 justor muscular scars (ad) and their path of advance is, as a whole, more 

 or less triangular, and situated one on each postero-lateral portion of the 

 valve. The front margin of the area is rather broad and divided into four 

 small, somewhat indistinct lobes; posteriorly the area contracts to the in- 

 itial point of the path of advance; two scars appear to be defined on the 

 anterior two-thirds of each area; they are elongate and include two of the 

 little lobes of the anterior margin within the area of each, and appear to 

 represent the point of attachment of the exterior and posterior adjuster 

 muscles; there is a small space divided off by raised lines that may be the 

 central adjustor scar, but it is not clearly denned. 



Between the areas of the adjustor scars and the large central area of 

 the adductors there is a sharp, narrow ridge that distinctly separates them. 

 A narrow elongate area (pp), outside of the area of the adjustor scars, was 

 probably the point of attachment of the posterior parietal muscle, and the 

 lateral and outer walls of the perivisceral cavity seem to have left evidence 

 of their presence on the margins (w} of the central area. 



The great pallial sinuses approximate quite closely towards the front, 

 curving gently outward and backward around the central area to opposite 

 the anterior margin of the area of the adjustor muscular scars, around 

 which they curve to the narrow margin just within the exterior border of 

 the shell; their further course cannot be traced, but, from the narrow area 

 between the posterior parietal area and the margin, the sinuses must have 

 been very narrow, and with very minute, if any, lateral or internal ramus- 

 cules. The anterior lateral ramifications of the sinuses are strongly defined 

 as they spring from the main sinus, becoming smaller and bifurcating or 

 branching towards the margin of the valve; no inner ramifications are to 

 be seen on the space (i) between the great sinus and the perivisceral area 

 on the dorsal valve, a feature, however, that is well shown on a fragment 



