BaJcer — The Molluscan Fauna of McGregor, Iowa. 253 



A single specimen has an irregular piece of shelly matter 

 extending from the anterior border of the posterior adductor 

 muscle scar 42 millimeters into the central cavity of the shell, 

 which measured 110 millimeters in length and 60 millimeters 

 in breadth. The shelly matter is hollow and contained mud. 

 15 millimeters anterior to this curious appendage a rounded 

 pearl has been formed. Another specimen has the whole 

 posterior end flattened. 



Lampsilis luteola Lamarck. 



Common. One out of three specimens contained pearly 

 matter or baroque pearls. 



Lampsilis ligamentina Lamarck. 



One of the most common shells. Out of fifty-one speci- 

 mens only four contained indications of pearly secretions. 

 The nacre varies from white to pink and salmon. Distorted 

 specimens of this species are common. 



Lampsilis orbiculata Hildreth. 

 Apparently rare. 



Lampsilis anodontoides Lea. 



Common. Twenty-five per cent contained pearls. 



Lampsilis fallaciosa (Smith) Simpson. 



Not common, apparently. The specimens from this locality 

 are brightly rayed ; one out of six contained pearly matter. 



Lampsilis recta Lamarck. 



Common. Large and fine. Only two specimens were 

 seen with pearly matter. The range of variation in nacre is 

 marked. Of fifteen specimens one was white, one salmon, 

 three mixed white and purple and ten were deep purple. 



Lampsilis alata Say. 



Common. A majority of the specimens contained pearly 

 secretions. One specimen had two pear-shaped lavender 

 pearls in the center of the shell near the hinge. Distortions 

 consisted principally of the flattening of one valve. 



