80 THE NAUTILUS. 



the whole coast. Abundant, both alive and dead ; fragile, white 

 and beautiful. 



Mulinia gaudeloupensis Recluz. Single valves on the shore at 

 Wounta Haulover. 



( To be continued.} 



NEW VARIETIES OF NORTH AMERICAN PISIDIA. 



BY V. STERKI. 



During the twelve years' study of our Pisidia, on about 350,000 

 specimens examined, many new forms were found. Some of them 

 have been published from time to time, since 1895, in the NAUTILUS, 

 others were held back, mostly for years, in the hope of getting ad- 

 ditional materials which would more clearly show their relations and 

 positions. Owing to the great variation of most of our species, with 

 some apparently endless, it is often difficult to know, or even to 

 estimate, whether a new Pisidium represents a new species, or a 

 variety, and it seemed preferable to be rather over-cautious with 

 regard to " n. sp." than too hasty. Yet new forms, more or less 

 different from those published or regarded as typical for a species, 

 should be named and described, and short descriptions of a number 

 of such are offered in the following lines. They are ranged under 

 species already known, as varieties, in many instances with some 

 doubts, leaving it for further evidence to prove their real affinities 

 or their claims to representing distinct species. A few short notes 

 are necessarily added, but a more detailed discussion of the affinities 

 etc., of the various species and forms is left for a forthcoming re- 

 vision of our Pisidia. 



Pisidium idahoense Roper var. indianense n. Smaller than the 

 types, less inflated ; beaks much narrower, low, little prominent over 

 the hinge margin ; surface with several well-marked lines of growth, 

 more horn-colored than in the other forms ; shell and hinge slight, 

 the right cardinal tooth less curved ; long. 8, alt. 7, diam. 4 mill. 



Hab.: Lake Maxinkurkee, Ind., collected in considerable num- 

 bers by Drs. Evermann and Bartsch, for the U. S. Fish Commission. 



As compared with the types from Idaho and the larger, much 

 inflated form from Seattle, Washington, the Indiana Pisidium ap- 

 pears to be of a distinct species. Yet a form, eventually a var., from 



