THE MOLLUSC A OF MUSCATINE COUNTY. 19 



have alread}- stated, under dorfeuillianus, that we cannot 

 find constant characters to separate the two species, if there 

 be two. Some say pustulosus is rare here. If so, then dor- 

 feuillianus is abundant. What we call pustulosus, from the 

 interior streams, seems to fill the figure and description of 

 schnolcraftensis of Lea in ''Observations." Vallatus (Lea) 

 is most likely found in the Des Moines, and, it may be, in 

 the Cedar. 



U. pyramidatus, LEA. Rare. Mississippi. Mytiloides (Raf.), as 

 figured and described in Conrad's " Monograph," is the same, 

 it appears to us, as Lea's pyramidatus. Nacre generally 

 white, sometimes pink. It is probable that some of our 

 shells catalogued as solidus (Lea) are pyramidatus of the 

 same author. Length, 8.5; breadth, 6.8; diam., 5.6cm. 



II. rectus, LAMARCK. Common. Mississippi, Cedar, Des Moines. 

 Nacre generally rose or pink, but occasionally white. 

 Weight, 8 oz. ; length, 14.5 ; breadth, 5.7 ; diam., 4.6 cm. 



U. rubiginosus, LEA. Rare. Cedar, Iowa, Des Moines. Nacre 

 light pink, or white. Length, 5.8; breadth, 4.5; diam., 

 3.4 cm. 



U, subovatus, LEA. Cedar. (See occidens.) Length, 13.4; 

 breadth, 8.4 ; diam., 3.6 cm. 



U. securis, LEA. Common. Mississippi. Young specimens are 

 very beautiful. Length, 9 ; breadth, 6.8 ; diam., 4 cm. 



U. solidus, LEA. Very rare. Mississippi. (See pyramidatus.) 

 It appears to us that solidus is the 3'oung of pyramidatus. 

 Length, 4 ; breadth, 3.7 ; diam., 3 cm. 



U. spatulatus, LEA. Very rare. Mississippi. We found one 

 live specimen, at this place, of what appears to be spatulatus. 

 The species is found at Davenport and New Boston ; but, with 

 this single exception, no shell has been taken here, among 

 the thousands we have collected, that will compare in the 

 least with examples received from Professor Pratt of Daven- 

 port, and Mr. Marsh of Aledo, 111. Our shell is very heavy, 

 much heavier than longer shells referred to aboA'e. It is very 

 much the shape of a }"oung ligament inus. Length, 5.6 ; 

 breadth, 3.2 ; diam., 2.4 cm. 



U. temiissimus, LEA. Ver}* rare. Mississippi. Burdett's Slough. 

 Substance of shell extremely thin. Sexual difference seems 



