THE NAUTILUS. 



VOJ,. XIII. APRIL, 1900. No. 12. 



THE GENUINE PLANOKBIS COEPULENTUS, SAY. 



BY BRYANT WALKER. 



The sound judgment and critical acumen of that great naturalist, 

 Thomas Say, has been exemplified not only in the large proportion 

 of his species which have withstood the scrutiny of the " higher criti- 

 cism " of the modern school of conchologists, hut also by the number 

 which in recent years have been rescued from the synonymical bone- 

 yard, to which they had been relegated by his immediate successors, 

 and restored to their original integrity. 



The fine species which he described in 1824 as Planorbis corpulen- 

 tus has been one of the most unfortunate of these forgotten species in 

 its scientific history. Owing, no doubt, in a large measure to its 

 extreme rarity, it has been constantly misapprehended, not only by 

 all the descriptive writers, but by nearly every one who has had oc- 

 casion to refer to it. 



The earlier American conchologists were unanimous in referring 



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to it unusually large specimens of P. trivolvis, and generally consid- 

 ered it a form of that species and doubtful, even, of varietal rank. 



In 1841, Haldeman referred to it a large Planorbis collected by 

 Nuttall, in the Lewis river, Oregon, and his example was followed by 

 Gould, Chenu, Clessin, Tristram ,and Sowerby. AV. G. Binney 

 (18Gf>) was " inclined to believe that Say had before him a form ot 

 P. trivolvis when he drew his description of P. corpulentus," and con- 

 sidered the west coast species referred to that form by Haldeman, 



