6 MEMOIRS OF THE CARNEGIE MUSEUM. 



General Distribution: This species is found, outside of North America, in 

 northern and middle Europe, northern Asia, and Japan (Simpson, 1900, p. 677).^ 

 With regard to this, we do not need to go into detail here. Its North American 

 distribution recently has been discussed by Walker (1910a, p. 140, pi. 2), and a 

 careful list of localities has been given, to which we should add, however, a few 

 new localities represented in the Carnegie Museum (see above), and further Buck- 

 field, Oxford Co., Maine (Allen, J. A., in Nautilus, XXV, 1912, p. 120) (See also 

 Nylander, 1914). 



I do not think that Margaritana margaritifera is of North American origin, 

 as represented by Scharff (1912, p. 51), but I believe that it reached eastern North 

 America by the North Atlantic land-bridge, coming from Europe (See Scharff, 

 ibid.). I also hold the opinion of Scharff that there were other places of survival 

 during the Glacial time, either within the drift area, or close to its eastern edge, 

 on the former eastward extension of the continent. 



Family UNIONID.S: (D'Orbigny) Ortmann (1911). 

 Ortmann, 1911a, p. 129; 19115, p. 335; 1912, p. 223. 



Subfamily UNIONIN.E (Swainson) Ortmann (1910).' 

 Ortmann, 1910, p. 116; 1911a, p. 129; 19115, p. 335; 1912, p. 224. 



Key to the Genera. 

 oi. All four gills serving as marsupia. Mantle connection between anal and supra-anal openings present, 

 short, and deciduous. 

 bi. Placenta; subcylindrical, rather persistent, often red. Shell smooth, without sculpture upon 



the disk. Beak-sculpture simple, concentric, and poorly developed Fusconaia. 



bo. Placentoe lanceolate and compressed, not very persistent, whitish, or yellowish, but not red. 



postglacial. This would indicate, possibly, a very early step in the postglacial dispersal of this species, 

 provided these shells are actually from the neighborhood of this cave, and have not been carried there 

 by man from a long distance. At jjresent, Margaritana is not found in this region. I have hunted for 

 it in vain in Broadhead Creek at Henryvillo (above Stroudsburg), and have received the assurance from 

 competent persons that nothing resembling this shell is found in the trout-streams within a radius of at 

 least fifty miles from Henryville. 



« It also has been reported from Iceland, but this has been questioned. The Carnegie Museum 

 has received from W. Israel a specimen labeled " Rej'kjavik, Iceland." After correspondence with 

 Israel and Stejneger (in Washington), and by Stejneger with parties in Copenhagen, there remains no 

 doubt that this specimen is to be traced back to a dealer in Copenhagen, who tried to impose upon a 

 number of conchologists. He even claimed that the specimens in (luestion were collected by Mrs. Israel 

 in 18G3, before she was born! 



' This subfamily cannot be credited to v. Ihering (1901, p. 53) since he used the name in an entirely 



different sense. 



