I9I3-] ORTMANN— THE ALLEGHENIAN DIVIDE. 363 



lantic dement, and this is a problem correlated with the Tennessee- 

 Coosa problem, and the connection of the Tennessee fauna with the 

 southern and southeastern drainage systems of the Appalachians. 

 It can be solved only after much more extended investigations in the 

 Gulf and Atlantic streams from Alabama to the Carolinas. 



This much is sure, that the existence of this southern element in 

 the Atlantic fauna is well established. Simpson (1893, p. 355) 

 already has indicated it clearly, and that it probably is connected with 

 the fauna of the interior basin around the southern extremity of the 

 Appalachians (see also Ortmann, 1905, p. 124). This center forms 

 part of Adams' (1902 and 1905) great southeastern center, but is 

 probably a rather sharply separated, and rather old subdivision of 

 it. It had, with regard to aquatic life, a northward route of dis- 

 persal, not only in Postglacial, but also in Preglacial times, on the 

 Atlantic slope. This route has been admitted by Adams (1905) for 

 land- forms, but has not been mentioned (/. c, p. 63) for aquatic 

 forms. 



Fact II., 2, (b). 



Another element of the Atlantic fauna seems to have its center 

 in the north (from Pennsylvania and New Jersey northward). The 

 following Najades belong here: Anodonta Cataracta, Anodonta im- 

 plicata, Alasmidonta varicosa, Lampsilis radiata, Lampsilis cariosa, 

 Lamp suis ochracea, 16 and the crayfish: Cambarus limosus. All 

 these forms have in common, that they are most abundant north- 

 ward, and advance southward either not at -all (Anodonta impli- 

 cata), or chiefly on the coastal plain. Only Alasmidonta varicosa 

 seems to be more universal in its distribution on the Atlantic side. 

 Lampsilis ochracea is a form of the lowlands (estuaries). Lamp- 

 silis radiata and cariosa, and apparently also Anodonta Cataracta 

 have a rather wide distribution in Pennsylvania, but southward they 

 seem to occupy only a narrow belt on the coastal plain. The same 

 is true of Cambarus limosus. However, our knowledge of the dis- 

 tribution of these forms in the lowlands of Virginia, and southward, 

 is rather unsatisfactory, but the fact is undeniable that, while these 



16 Margaritana margaritifera and Enrynia nasuta resemble these to a de- 

 gree, but, as we shall see below, are peculiar in other respects. 



