No. 1610. NEW PACIFIC COAST MOLLUSKS—DALL. ASS 
grooving of the valves in ensifera is comparatively feeble, toward the 
ends especially, compared with that of scissurata, which is not only 
stronger but covers the whole valve except a small portion near the 
posterior end, while in ensifera both ends are usually free from 
grooves; but Professor Kelsey has dredged in 80 fathoms, off the 
entrance to San Diego Harbor, a variety which, while agreeing in 
form and hinge characters with ens¢fera, has the grooving extended 
to within 6 millimeters of the posterior extremity and over the whole 
anterior end in specimens 28 millimeters long, all of the specimens 
showing similar extension of the sculpture, while a large series from 
San Pedro to the Aleutian Islands does not afford a single instance 
of such extension. It seems, therefore, that the difference is marked 
enough to constitute a namable variety which may take the name of 
plena. 
Proc. N. M. vol. xxxiv—08 7 
