22 THE MOLLUSC A OF MUSCAT 1NE COUNTY. 



shells that agree in every particular with Lea's figure and 

 description ; but they do not agree with examples called decora 

 from Ohio. We have heretofore regarded these the 3~oung of 

 grandis. Substance of shell very thin ; hinge margin straight, 

 and slightly winged back of umbones ; epidermis light about 

 beaks, gradually becoming darker, and terminating in a black 

 or nearly black band, about midway from beak to basal mar- 

 gin, parallel with lines of growth, the remainder green with 

 rather indistinct rays of lighter color ; tumid. This must be 

 the shell that Lea called decora. Length, 9.6 ; breadth, 6.1 ; 

 diam., 4.7 cm. 



A. edentula, LEA. Rather rare. Mississippi, Cedar, Mud 

 Creek, Des Moines. In the " Natural History of New 

 York" DeKay figures and describes a form unadilla, which 

 Lea, in his " Synopsis," gives as a synonyme of edentula. De- 

 Kay, in the same work, figures and describes edentula. The 

 latter maybe Say's undulata; but we can see no difference 

 between edentula and undulata. Edentula is an exception 

 among the species of the genus as to its habitat. So far, we 

 have found it in our rivers only ; whilst all the others are 

 limited to our ponds and sloughs, except, it may be, ferussa- 

 biana, and occasionally a specimen of grandis, which we find 

 in the Mississippi. Substance of the shell is much heavier 

 than any other of the sub-genus we have seen ; anterior hinge- 

 tooth quite prominent in some shells ; nacre generally salmon ; 

 muscular impressions very distinct ; epidermis dark brown. 

 Length, 8.1 ; breadth, 5 ; diam., 3 cm. 



A. ferussaciana, LEA. Mad Creek, Des Moines, Honey Creek in 

 Delaware County. A few "dead" shells have been found 

 in Mad Creek along with M. deltoidea. We have found live 

 shells at Des Moines ; but the finest are from Honey Creek, 

 where it appears to be common. We have examples from this 

 place and Des Moines that are apparently the same as wardi- 

 ana (Lea). A study of Lea's figures and descriptions of 

 these species, together with specimens, inclines us to believe 

 them the same, or, at most, that the latter is a variety of the 

 former. Shell from Honey Creek measures, length, 8.1 ; 

 breadth, 4 ; diam., 3 cm. 



A. grandis, SAY. Very abundant in Keokuk Lake, and in our 



