42 THE NAUTILUS. 



NEW NORTH AMERICAN PISIDIA. 



BY V. STERKI. 



Pisidium ashmuni n. sp. 



Mussel somewhat elongate, moderately inequipartite; scarcely ob- 

 lique, moderately inflated; superior and inferior margins moderately 

 curved, supero-anterior slope curved down to the rounded anterior 

 end situated well below the median line ; [posterior end subtruncate, 

 with more or less of an angle at the scutum ; beaks somewhat pos- 

 terior, rather broad, rounded, moderately elevated over the hinge 

 margin ; surface shining, with microscopic, shallow, rather regular, 

 crowded striae, and one or a few impressed lines of growth • color 

 pale horn, shell translucent, thin ; hinge slight, plate narrow; cardi- 

 nal teeth rather long, fine, lamellar, the right curved with its an- 

 terior end much shorter and situated much higher up on the plate 

 than the posterior which is somewhat thickened ; left anterior of the 

 same shape as the right, rather hook-like at its anterior end, the 

 posterior oblique, slightly curved and passing over about two-thirds 

 of the anterior ; lateral teeth rather long, produced far beyond the 

 pointed cusps; outer laterals of the right valve slight but distinct; 

 ligament rather slight. 



Size: Long. 2.8, alt. 2.3, diam. 1.6 mill. 

 Long. 2.3, alt. 1.9, diam. 1.4 mill. 



Most specimens are intermediate. 



Habitat: San Rafaels, New Mexico, collected by Rev. E. H. 

 Ashmun, in whose honor the species has been named. 



Pis. ashmuni ranges under the abditum group. It is easily recog- 

 nized, being of about the same size with Pis. splendidulum St. It is 

 more elongate and its beaks are broader. 



Pisidium danielsi n. sp. 



Mussel slightly inequipartite, moderately and regularly inflated, 

 outlines nearly short oval ; all margins well curved, or the posterior 

 subtruncate, anterior end rounded, rather below the median line; 

 angles at the scutum and scutellum not marked in most specimens, 

 slightly so in some ; umbones little posterior, low, slightly projecting 

 over the hinge margin, moderately broad, each with a depression be- 

 low the apex and above a slightly raised, concentric ridge ; surface 

 with somewhat coarse, subregular and sharp stride, and a few coarser 



