42 THE NAUTILUS. 



corpulent. It has been identified as corpulentus Say, but this is a 

 totally different species, the cbaracters of which have been very fully 

 described by Mr. Bryant Walker in a previous volume of the 

 Nautilus. 



It would be interesting to know the exact range of binneyi, and I 

 would suggest that conchologists generally examine their collections 

 for this species, sending the information to either Mr. "Walker, of 

 Detroit, or to me (or to both of us). 



A large amount of exact data is needed to accurately determine 

 the range of the various species of fresh-water pulmonates, and a few 

 notes on this magnificent Planorbis will aid materially in this direction. 



PISIDIUM MAECI, N. SP. 



BT V. STERKI. 



Mussel rather small, well inflated, high, slightly inequipartite and 

 oblique, with outlines well rounded; superior margin short, nearly 

 straight, with a rounded angle at its posterior end and a very slightly 

 marked one at the anterior; posterior and inferior margins forming 

 one regular, nearly circular curve, supero-anterior slope slightly 

 marked; beaks little posterior, large, somewhat flattened, well promi- 

 nent; surface shining, with medium fine, irregular striae and several 

 distinct lines of growth, the upper one marking off the nepionic 

 mussel (as in Musculiuvi); color straw to yellowish-horn,^ with 

 slightly marked lighter and darker zones; hinge short, rather slight, 

 but well formed, with a short ligament, plate narrow; cardinal teeth 

 somewhat curved; the right one moderately long, its posterior part 

 thicker and grooved ; left anterior very short, " high," abrupt, thin, 

 the posterior almost longitudinal, twice as long as the anterior, less 

 " high," slightly thicker and grooved in its posterior part; lateral 

 cusps short, pointed, the outer ones of the right valve smaller but 

 distinct, not pointed. 



Long. 3.5, alt. 3.4, diam. 2.5 mm. 



Habitat: Mt. Leidy, Utah, at 10,000 feet, in a stagnant pond, 

 collected by Mr. Marcus H. Dall (son of Dr. Wm. H. Dall), in whose 

 honor the species is named, on September 18, 1905. 



This Pisidium appears not to be closely related to any of our 



^ Most specimens appear brownish from the dried soft parts. 



