210 Annals of the Carnegie Museum. 



south. The distribution of the two Anodontas also should be investi- 

 gated more closely. Alasmidonta hetorodon appears to be restricted 

 to the southeastern corner of the state. Margaritana margaritifera 

 should be looked for in the northeastern and the northern central parts 

 of the state. The establishment of the southern boundary of distribu- 

 tion of the latter species is very desirable. Unio fisheriaitus is a 

 southern form, and may be present in the Potomac drainage in south- 

 ern Pennsylvania. Unio p?-oducttis Conrad, which comes very near 

 to U. fisherianus, is known from the northern tributaries of the 

 Potomac in Maryland (Pilsbry). The occmx^x^c^ oi U. fisherianus 

 in White Clay Creek and in the Schuylkill probably marks the northern 

 extremity of its range. From the Susquehanna it is unknown. 



Thus we see, that many questions still await final decision, and 

 that much remains to be done in a section of the country, where 

 collectors have been busy for almost a century. Before we know the 

 actual distribution of each, species, we cannot venture to say anything 

 about their history ; but this should be the aim of all studies in geo- 

 graphical distribution. 



