NAIADES OF MISSOURI 23 



both valves; scars deeply impressed; beak cavity narrowly deep; 

 nacre silvery white; male shell usually more compressed than 

 that of female, but no true dimorphism shown. 



Length Width Diameter Um. ra. Locality. 



75 X 63 X 48mm 0.16 (Miss. R., LaGrange, Mo.) 



70 X 64 X 49mm 0.78 ( " " " " 



55 X 43 X 39mm 0.17 (Meramec, R., Fern Glen. Mo.) 



60 X 55 X 46mni 0.17 (Osage R., Linn Cr., Mo.) 



Juvenile Shells are described as having a light yellowish 

 brown epidermis with green rays most distinct on anterior slope, 

 and finely ribbed lines running from beaks to ventral margin 

 across center of disk. 



Miscellaneous Remarks: — This species was hidden in syno- 

 nomy for many years until Mr. Bryant Walker (1910b, p. 5) 

 brought it to light through diligent study. It is found in most 

 typical form in the Mississippi River and occasionally it mav be 

 found in the Meramec and Osage Rivers where it is to be distin- 

 guished from F. fiava by its swollen high beaks and darker epi- 

 dermis. Then, too, this species is determined largely ecologically, 

 being an inhabitant of the large streams and deep water, for the 

 most part. In most of the interior streams of the state, undata, 

 however, is found chiefly in an intermediate, or intergraded, 

 form with fiava. In the whole southwest this species does not 

 seem to be very near the type as found in the Ohio drainage or 

 in the Upper Mississippi, especially in Wisconsin where Barnes 

 secured his type lots. The Des Moines River, Clark Co., Mo., 

 has produced rather good types, some shells of which have been 

 sent to the National Museum by Mr. B. F. Bush and are now 

 on exhibit there under the number 132, 633. However, none of 

 these so-called undata types come up to those of the Upper Miss- 

 issippi. Surber (1913, p. 113) finds F. undata in the larval state 

 to be a gill parasite on the black crappie {Pomoxis sparoides) as 

 an occasional host. Undata is a tachytictic form, but begins its 

 breeding very early, bearing glochidia June, July and August 

 and hence has an unusually long period for a summer breeder. 

 The writer has observed that during the first part of the breeding 

 season, when the ova are bright carmine color, that not only the 

 marsupium but also the nutritive parts— especially the foot are 

 also a brighter color — chiefly orange — than at the end of the season 

 when most of the anatomy has a brownish or soiled white color. 



