I9I3.] ORTMANN— THE ALLEGHENIAN DIVIDE. 325 



tribution might be more northern, but this may be due to defective 

 knowledge of the facts. 



V. Another group of Atlantic species Jias closely allied species 

 in the interior basin. No. ly of the list, Eurynia {Micromya) con- 

 stricta, has a representative form in the upper Tennessee drainage 

 {Eurynia {Micromya) vanuxernensis) . Six others (nos. 8, 9, 14, 

 19, 20, 21) have closely related, indeed representative forms, in the 

 upper Ohio drainage. The relation is as follows : 



no. 8 and 9, Anodonta cataracta and implicata, represent the 



western Anodonta grandis. 

 no. 14, Alasniidonta varicosa, represents the western Alasmi- 



donta marginata. 

 no. 19, Lampsilis radiata, represents the western Lanipsilis 



liiteola. 

 no. 20 and 21, Lampsilis cariosa and ochracea, represent the 



western Lampsilis ovata ventricosa (and its allied forms). 

 It should be noted that just these Atlantic forms are preemi- 

 nently those wdiich have a more northern range upon the Atlantic side. 



VI. Finally, there are four species on the Atlantic side, zvhich are 

 specifically identical zmth western forms. Particulars are as follows : 



no. 13, Alasniidonta marginata susqnehannae, is a local form of 

 the Susquehanna drainage, closely resembling the widely dis- 

 tributed western Alasniidonta marginata. 



no. 7, Syniphynota tappaniana, is represented on either side by 

 an absolutely identical form. But here the distribution is 

 rather general on the eastern side and local on the western 

 (New River). 



no. 16, Strophitus edentulus, is absolutely identical on either 

 side, and also widely distributed, east as well as west. But 

 it should be noted that it is apparently absent in New River. 



no. 18, Eurynia nasuta. Here we see that the identical species 



is on the Atlantic side and in Lake Erie basin, but not in the 



upper Ohio drainage. 



We see at once that these cases apparently are not subject to the 



same laws, and further below they shall be treated each by itself. 



There remains yet one of the Atlantic forms, no. 15, Strophitus 



