140 THE NAUTILUS. 



Strephona literata, Tuomey & Holmes, Pleioc. Foss. S. C., p. 

 140, 1857. 



Olivancillaria ( Utriculina) litterata, H. & A. Adams, Gen. i, 

 p. 141, 1858. 



Dactylina carolinensis, Conrad, Pro. Ac. Nat. Sci., p. 563, 1862. 



Oliva circinata, Marrat, Thes. Conch., iv, p. 21, 187 1. 1 



Olivet litterata, (0. Sayana. Rav. ) Ravenel, Cat., p. 16, 1874. 



PLEUROBEMA MISSOURIENSIS MARSH. 



BY BRYANT WALKER. 



This species was described by the late William A. Marsh in 

 1901 in THE NAUTILUS, xv, p. 74. The types were collected by 

 the late Ellwood Pleas in the Black River near Poplar Bluff, 

 Butler Co. , Mo. It has not as yet been found by any other 

 collector. It was not figured by the author, and owing to this 

 fact and the rather unfortunate comparisons with other species 

 made in the remarks accompanying the description, it has 

 always been a conundrum to other students of the Unionidse. 



After Mr. Marsh's death in 1913, his collection of Unionidse 

 was acquired by Mr. L. S. Frierson and myself. The four 

 specimens of missouriensis mentioned by Marsh were found and 

 the type and one other are now in my collection. The other 

 two belong to Mr. Frierson. 



The specimen now figured (pi. V, figs. 1, 2) is marked 

 "Type" on the interior of the right valve. 



The examination of these specimens shows that the systematic 

 position and relationship of the species was misunderstood by 

 Mr. Marsh. 



Missouriensis is not a Pleurobema, but is a Quadrula of the 

 subrotunda group as defined by Simpson. It has no resem- 

 blance to P. bigbyense Lea at all. The comparison with P. hart- 

 manianwn Lea is equally fallacious and would seem to have 

 been based upon a misapprehension of that species, for which, 

 perhaps, he is not to blame. Hartmanianum is restricted to the 



1 Fide Johnson. 



