312 The Ohio Naturalist [Vol. V, No. 6, 



10. Ptychohranchus phaseolus Hildreth. Ohio, Tennessee and 

 Cumberland River systems; peninsula of Michigan; Kansas; 

 Arkansas; Indian Territory; Louisiana. 



11. Strophitus edentulus Say. Entire Mississippi drainage; 

 St. Lawrence system and south in streams draining into the 

 Atlantic to North Carolina; north in the British possessions to 

 Lake Winnipeg ; southwest to central Texas ; Tyner, Alabama. 



12. Pegias jabula Lea. Cumberland and Tennessee river 

 systems. 



i;3. Alasmidonta t nut cat a B. H. Wright. Upper Mississippi 

 drainage; Ohio, Cumberland and Tennessee River systems; 

 Michigan; Upper St. Lawrence drainage. 



1-1. Unio gibbosus Barnes. Entire Missippissi drainage; St. 

 Lawrence and its tributaries; Alabama River system; southeast 

 into Florida; southwest to the Guadalupe River, Texas. 



15. Pleurabema clava Lamarck. Ohio, Cumberland and 

 Tennessee River systems. 



16. Quadrula coccinea Conrad. Entire upper Mississippi 

 drainage ; St. Lawrence basin in various localities. 



KEY TO THE LIVERWORTS RECOGNIZED IN THE SIXTH 

 EDITION OF GRAY'S MANUAL OF BOTANY. 



Edo Cl.\assex. 



This key was prepared for the purpose of making the work of 

 determining the liverworts described in Gray's Manual more 

 easy than it has been heretofore. Other characters have been 

 added to the description of the perianth, here and there, that in 

 case the perianth is wanting, it may be possible to find the name 

 of the genus of the specimen in hand. 



In the archegonial "fiow^er" of the foliose liverworts the ped- 

 icel together with the capsule is usually surrounded by three 

 envelopes — the involucre, the perianth, and the calyptra. 



The external envelope, called the involucre, is formed by the 

 uppermost Reaves which surround the base of the perianth. They 

 usually differ from the lower leaves by their size and shape and 

 are sometimes more or less connate with the perianth. 



The perianth, surrounded by the involucral leaves, is a sac- 

 like envelope of oval or cylindrical form. It may be compressed 

 or angular, smooth or folded and its orifice may be either entire 

 or lobed, dentate or ciliate. Although usually present it is want- 

 ing in Gymnomitrium and most of the frondose liverworts. 



After fertilization the ca])sule is formed in the interior of the 

 archegonium and while develo])ing ru])tures the upper part of 

 the same by the lengthening of its pedicel. The archegonium 



