Sterki: Some Notes on Sph/Eriid.e. 429 



and comparison before reporting upon them. It is worthy of obser- 

 vation that the Pacific region from Alaska and British Cohimbia to 

 southern California is remarkably rich in Sphxriidae, most of them 

 being different from the eastern species. Every sending from the 

 western coast reveals new forms. The fauna as a whole is still in- 

 sufficiently and only fragnientarily known. Some of the species ap- 

 pear to be so variable that it is difficult to define them. In conse- 

 quence I am in doubt whether some of them represent local forms, 

 regional subspecies, or distinct species. I may add that there are in 

 my hands some manifestly new and distinct species, which are not, 

 however, represented by sufficient numbers of specimens to justify 

 me in publishing them as such for the present. This fact may mean 

 disappointment to the collector who has sent in his specimens and 

 requests that they be " named." Nevertheless every good lot of speci- 

 mens from the Pacific coast, or, for that matter, from any locality 

 whatsoever, means a contribution to the understanding of the interre- 

 lations of the species and forms of this intricate group of the 

 Pelecypoda, their variation, and their geographical distribution. 



Descriptions of New Species and Forms of Pisidium and 



Sph.erum. 



I. Pisidium dcflcxnm n. sp. Mussel inequipartite, oblique, well in- 

 flated, anterior part markedly larger and directed downward, the 

 superior and inferior margins being at an angle ; superior margin 

 slightly curved and merging into the anterior in a rather long con- 

 tinuous curve as far as the rounded anterior end. which is well below 

 the median line; posterior margin truncate or subtruncate obliquely 

 anteriorly, forming a well-marked angle with the superior, passing 

 into the inferior margin without an angle ; beaks rather posterior, 

 broad, rounded, or slightly flattened, not greatly projecting over the 

 dorsal margin ; surface dull glossy, with fine, somewhat sharp and 

 irregular striae and a number of rest-lines; color grayish to yellowish 

 corneous, alternating with narrow dark zones, mostly along the rest- 

 lines; shell rather thick, opaque; hinge stout, somewhat like that of 

 compressinn, but the plate is longer and the laminae, especially the 

 anterior, diverging at smaller and more rounded angles; the right 

 cardinal is less sharply curved, with a deep excavation below. Long. 

 3.5 ; alt. 3 ; diam. 2.3 mm. 



