16 THE MOLLUSC A OF MUSCATINE COUNTY. 



Found also in Mississippi, creek at Brown's Ferry on Cedar, 

 Mud Creek at Wilton, Des Moines River at Des Moines, 

 Skunk River at Ames : in fact, it is our most widely dis- 

 persed species. No little confusion exists concerning this 

 species. There are at least two well-marked forms here, and 

 I am inclined to say three. If we limit the species to those 

 having numerous fine undulating lines on the beaks, we shall 

 include siliquoideus (Barnes) and luteolus (Lam.), and exclude 

 a form with but two or three coarse folds about the beaks, 

 which we believe may be called ventricosus (Barnes) ; but the 

 figure of this species in American conchology is nearer to our 

 occidens (Lea). Siliquoideus has been abandoned by Lea. 

 This would leave the first group to luteolus. Of the long, 

 narrow, and generally thin examples, with numerous undula- 

 tions about the beaks, those from creek near Brown's Feriy, 

 Skunk, and Des Moines, are much smaller in every wa} r , 

 umbones very low, and epidermis with few and small green 

 rays over the light-yellow ground. The largest of this group 

 measures as follows: length, 7.8; breadth, 4.4; diam., 2.2 

 cm. Those from Muscatine Slough and Mud Creek are much 

 larger ; umbones very prominent ; green ra}*s generally nu- 

 merous and broad ; old specimens nearly black. Some ex- 

 amples are very beautiful. Length, 11.3 ; breadth, 6 ; diam., 

 4.5 cm. In both groups there are thin forms, narrow and 

 rounded, or somewhat pointed posteriorly ; and short, tumid 

 forms, wider, and truncated posteriori}'. An example of the 

 latter form measures, length, 9.6; breadth, 5.8; diam., 6.2 

 cm. These are, no doubt, sterile and fertile forms. 



U. metanevms, RAF. Common. Mississippi and Cedar. We 

 have a rare form, with few or no tubercles, and with a very 

 prominent lobe, gradually increasing in width from the um- 

 bones to the posterior basal margin. Length, 6.7; breadth, 

 5.5 ; diam., 4.5 cm. 



U. monodontus, SAY. Mississippi, near mouth of Geneva Creek, 

 and on sand-bar opposite Mr. B. -Hershey's mill, we have 

 found a few " dead " shells. Those at the latter place were 

 nearly fresh. No live shells have been secured, so far as we 

 know, nearer than Davenport. Length, 12.5; breadth, 4.8; 

 diam., 3 cm. 



