Baker — The Molluscan Fauna of McGregor, Iowa. 258 
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. 
