474. BR. P. Whitfield—Lingqula in the Trenton Limestones. 
surface by the growth of the animal to interfere with their dis- 
tinctness, this would scarcely be looked for in a fossil species. 
On the cast of the dorsal valve (fig. 1) the impressions of the 
pallial sinuses (ys) are deeply marked and are widely sepa- 
rated, leaving the area within them very considerable; the 
central or inner ramifications (1) are very distinct, and the 
outer ones also for a short distance from the main branches; 
while the posterior branches (2) show the lateral ramifications 
only on the outer side. The divaricator muscular scar of the 
dorsal valve (d) is very large and curved forward at the sides, 
being situated well back near the apex of the valve. It has 
not been satisfactorily observed on the ventral side, as every 
specimen yet obtained has been more or less imperfect at this 
point, but it-should be situated directly opposite that of the 
dorsal. The anterior adductor scars (aa) are small and situa- 
ted near the center of the valve, while the posterior adductors 
(pa) are large and situated outside of, and’ posterior to them ; 
so as to inclose their posterior ends. The scars of the adjustor 
muscles are distant from each other, and placed just within the 
posterior third of the length of the shell. Two elements can 
1 scar on some individuals, but they are 
dle and on the aap ited half occupy nearly the same relative 
e dorsal side. Near the center of the valve 
