1886.] PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 309 



of porcelanous white and almost polished, with uo visible epidermis aa 

 in fresh and living specimens of the latter shell; the variety midden- 

 dorffii is shorter and higher and somewhat more inflated. In the alco- 

 holic specimens the siphons of middendorffii are much longer than those 

 of the ordinary form. The inner margin of the pallial sinus in the right 

 valve is, in the specimen figured, nine millimeters distant from the an- 

 terior adductor scar; in the left valve they are only one and a half mil- 

 limeters apart. This specimen is 40.0™™ high, 45.0™™ long, and 20.0™™ 

 in greatest diameter. The figure is somewhat less than natural size. 

 This variety is rare and probably a race due to some peculiar environ- 

 mental conditions, such as, perhaps, a habitation in pure, clean, fine 

 sand or other circumstance peculiarly favorable to fine growth, com- 

 pactness of form, and hardness of shell. I have had it only from the 

 southern part of Bering Sea, St. Paul Island, Bering Island, Hagmeister 

 Island, and Nunivak Island, all localities where deep water and a clean 

 sandy bottom are the rule. It may be that in muddier localities it de- 

 velops into the calcarea or lata. 

 Washington, February 4, 1886. 



