PROCEEDINGS OF THE NATIONAL MUSEUM. 339 



j^umerous species of Naiades no doubt i)uslied up from tlie ]\Iissis- 

 sii)pi basiu into tbese lakes, and Avhen tbe ice cap finally melted tbey 

 occupied much of tlie area of tbe Mackenzie and St. LaAvrence systems. 

 Utiio margaritiferus, wbicb is circumboreal, is not knowu to exist in 

 tbe central Britisb American region, but is found in eastern Canada 

 and New England. It is quite probable, as lias been suggested by 

 Wetberby,' that this species may have extended across tbis wbole area 

 iu pre-Glacial times; tbat tbe onward movement of tbe ice cap exter- 

 minated it in tbis central area, and tbat it was driven soutbward to tbe 

 east of tbe Appalacliian cbain, wbere it still survives, Tbis ice cap 

 may liave also driven ont and destroyed nuicb of tbe Atlantic drainage 

 fauna, wbicb was afterwards replaced by tbe more vigorous Missis- 

 sipi>i Valley forms.'- Tbe Atlantic drainage group of Anodontas 

 typified by A. ffuriatilis seems to be closely related to tbe Cyf/nea 

 group, and may have been separated from tbe latter by tbe ice 

 sheet. 



In the Old World, Iniio and Anodonta are believed by Ludwig ' to 

 date back to tbe Carboniferous. The forms which be refers to these 

 genera are from Ithenish Westphalia, and are small, oval, oblong shells, 

 one of which has sulcations on the beaks. From the figures of the 

 binges, I greatly doubt whether tbe species referred to Fnio belong to 

 that genus. The few Unionidiie known from the Old World Jurassic 

 and Cretaceous strata do not seem to show decided relationships with 

 any other Naiad fauim. Spathu {jalloprorineialis, Matberon, which was 

 described by its author as a Unto, is believed by Sandberger to belong 

 to tbe former genus. ^ 



In the fignres of tbis species given by tbe author, the shell bears 

 some resembUmce to a Spatha,hut is very different from any species I 

 know of belonging to tbat genus, in the cbaracter of the beak sculpture. 

 In Spatha, the nmboes are smootli or nearly so, as are the shells of tbe 

 Mutelida^ in general. This species has strongly concentricall.y sculptured 

 beaks, the ridges ending in a very sharp angle posteriorly. It may 

 possibly be a Leguminaia. 



Several fossil Unios are known from Siberia and India, from what 

 are believed to be Tertiary strata. These resemble the solid fornjs of 

 China and the Mississipi^i Valley, and Unio bituhercuUdus, v. Marteus, 

 from tbe former country, is very mucb like Unio perplexus., Lea, from 

 the Ohio Eiver.^ 



In examining tbe fossil Tertiary Naiades of eastern Euroi)e, one can 

 not help noticing the wonderful resemblance of certain forms to well- 

 known groups in the Mississipxu Valley. Eegarding these species and 



' Joaru. Cin. Soc. Nat. Hist., July, 1881, p. 7. 



^See paper by the writer in Proc. U. S. Nat. Mns., XVI, pp. 991-995. 

 ^Palaeontogr., VIII. Die Najiideu der Rheiniscli-Westplialisclioii Steinkoblcn- 

 Formatiou. 



^ Land uud 8iisswasser Conch, der Vorwelt, p. 9">. 



' See Abdr. d. Zeitsch. deut. geol. Gesellschatt, 1S74, p. 74S. 



