■;'■! 



10 THE NAUTILI'S. 



.'!. /'is. milium Held, conforming with European specimens, have 

 been collected in Straits Lake, Michigan, by Mr. Bryant Walker, 

 and in Dallas Lake, Stearns County, Minn., by Mr. H. E. Sargent. 

 Among a number of fossils from a marl bed in Tuscala County, 

 Mich., also collected by Mr. Walker, there was one valve of the 

 same species. 

 ■ 4;. *In Aroostook County, Maine, Olof O. Nyhih'deT ■ has found V 

 few specimens of x» Pisidium ide j aJgcal witn-ionertToiB England flamed 

 milivin Held, which, however, Mr. Clessin says, is not that species. 

 It isofsomewhal the same shape and color, but larger and the*beaks 

 are more promineut. 



The question whether these Pisidia be native or introduced is an- 



- 

 sneredj at least for milium, by the fossil found. As to Mo. 4, an im- 

 portation is rather improbable, from its habitat. Eor Ni>s. 1 and 2 

 the possibility of a colonization cannot be denied, just as Ritiiynia 

 tentaculata has immigrated from -Europe, and, on the other mWl, 

 Calycvlina transversa Say seems to have been transported into I^jg- 

 land. Further researches are very desirable, and also fossils should 

 be secured wherever such may be obtainable. 



5. Pis. contortum Pr. This Pisidium has been described, in 1852, 

 as a fossil sp. from Massachusetts, and has lately been collected 

 from marl beds in Maine by Mr. Nylander, and in Michigan, by Mr. 

 Walker. Last year Mr. Nylander succeeded in finding a few recent, 

 living specimens, in Aroostook Co., Me. The shell is transparent, 

 of a deep wine or amber color, the surface highly polished. 



6. Pis. mediavmn, n. sp. Mussel of rather small size, elliptical in 

 outline, much inflated, often of somewhat irregular growth; superior 

 and inferior margins moderately curved, posterior well rounded, or 

 with a slight angle above, anterior rounded or slightly truncated ob- 

 liquely; beaks rather in the middle, slightly directed toward the 

 posterior, rather high, prominent over the hinge margin ; scutum 

 and scutellum very slightly marked; surface with very fine, crowded 

 stria?, somewhat shining, light horn to yellowish or straw colored ; 

 shell thin, nacre colorless, muscle insertions barely perceptible; 

 hinge fine, plate narrow ; cardinal teeth lamellar, slightly curved, the 

 right one in its posterior part somewhat thicker, simple or with a 

 fine, longitudinal groove; lateral teeth pointed, the outer ones of the 

 right valve comparatively large ; ligament fine, long. 2.5 to 3.5, alt. 

 -2.it to 2.8, diam. 1.7 to 2.3 mill. 



