114 THE NAUTILUS. 



Length, 3; height, 1.8; diameter 1.6 (inches). 



Length 76, height 51, diameter 40 mm. 



Found by Mr. W. H. Over, at Ulvers Point, Clear Lake, Deuel 

 Co., South Dakota, July 1, 1909. 



To launch a new Anodonta is a perilous undertaking, but in this 

 instance the novelty of the form is unmistakable. The beaks ally 

 the shell, of course, to Anodonta grandis, Say. It is nearest to 

 that form called by Mr. Antliony A. snbgibbosa (and especially to 

 the figure of this species shown in the Conchologia Iconica, which is 

 much more characteristic than the figure in the American Journal 

 of Conchology). From any form of Ano. grandis it differs in being 

 more cylindrical, i. e., in lacking the swelling " amidship " so often 

 shown by A. grandis; in being rayless (so far as known), but especi- 

 ally by having its posterior point not elevated above the basal line, 

 and by the marked truncation posteriorly, which truncation is as 

 marked as in Morgaritana morginata Say, and the straight posterior, 

 and the resulting quadrilateral aspect of the shell. It is more 

 quadrate than Anodonta doliaris, Lea. The lack of any ohh'quity is 

 remarkable. Mr. Over also sent me from the same lake examples 

 of Anodonta grandis, Say, and the facies of our species was strik- 

 ingly dissimilar. 



A NEW SYSTEM OF THE UNIONIDAE. 



BY DR. A. E. ORTMANN, CARNKGIE MUSEUM, PITTSBURGH, PA. 



Since October, '09 the present writer has been engaged in the 

 study of the anatomy of the soft parts of the Unionidob of Pennsyl- 

 vania, collected during the last four years. The material at hand 

 being very rich, it was possible to make out the structure of most of 

 our species, and the results obtained are rather satisfactory, and are 

 apt to furnish new principles for the systematic arrangement of the 

 species. 



Simpson (Pr. U. S. Nat. Mus. 22, '00). in his system, has indi- 

 cated some of the essential principles of classification, in fact, the first 

 pointed out the most important feature, the shape of the marsiipium, 

 Yet this system must be changed considerably, if it is to represent 

 the natural atHnities. This is due chiefly to the fact, that Simpson. 

 on the one hand, had ratiier insufficient material, and on the other, 

 that he did not go into microscopic detail. 



