174 ANNALS OF THE CARNEGIE MUSEUM. 
the specimens examined is over 50 pr. ct. of the length, and the nacre 
frequently is salmon-color or pink. 
*22. Pleurobema cordatum coccineum (Conrad): R; G. 
Given by Price (as Quadrula coccinea), and represented in the 
Walker collection from Greensburg, but not among the shells collected 
by Clench at this place. I have seen two specimens from Rio, with 
the diameter 47 and 49 pr. ct., thus standing close to catillus. Prob- 
ably more abundant in smaller streams and headwaters. 
*23. Pleurobema cordatum pyramidatum (Lea): Mm; O. 
In the Walker collection from Green River, Woodbury, Butler Co. 
Also listed by Price (as Quadrula pyramidata). It is not rare where 
I found it, with red or white nacre, and very typical in shape. 
*o4. Pleurobema clava (Lamarck): O; B. 
Also reported by Price. JI found only a few specimens, but they 
were very typical. 
*25. Elliptio crassidens (Lamarck): Mm; R. 
In Price’s list, “‘ Unio grandiferus Lea’ stands where this species 
should be expected, but it is hardly possible that it was intended (see 
above, under Cyclonaias tuberculata granifera). This species is rare 
at Mammoth Cave, as well as at Rio, and has not been found else- 
where. 
*26. Elliptio dilatatus (Rafinesque): Mm; O; Mf; R; C; D; B; S. 
Also recorded by Price (as Unio gibbosus Barnes). Simpson (1914, 
p- 600) gives Unio gibbosus armathwaitensis Wright from ‘‘Mammoth 
Cave, Green Co., Ky.,’’ but Mammoth Cave is not in Green Co. U. 
armathwaitensis is an entirely superfluous name, and an absolute 
synonym of dilatatus.* This species is common in Green and Barren 
3 The Carnegie Museum has topotypes of armathwaitensis from ‘Branch of 
South Fork Cumberland, Armathwait, Fentress Co., Tenn.’ (probably Clear 
Fork, above Rugby), and many specimens from another stream in this vicinity, 
New River, Scott Co., Tenn. (collected by myself Aug. 30, 1924). All these are 
normal dilatatus, and the diagnostic characters given for armathwaitensis (‘shell 
narrower in front, widest behind, subcompressed, subsolid’’) are not at all evident. 
In fact, these are individual characters, which may be found anywhere among 
typical specimens of dilatatus. 
