THE NAUTILUS. 141 



Wyoming ; or at the beak sculpture of a number of species described 

 by Wliitiield from tlie Laramie of Montana (see : Bull. Amer. Mus., 

 N. H. 19, '03 p. 483 and 23, '07 p. 623), we cannot deny, tliat we 

 have here a beak sculpture corresponding very closely to the " radial " 

 sculpture of certain Asiatic types. This is especially true in : U. 

 retusuides Whitf. ('03, pi. 38, fig. 6), U. hrowni Whitf. {ibid. pi. 38, 

 fig. 3), U. percorrv gains Whitf. {ibid. pi. 40, figs. 3, 4), and U. 

 pyramidatoides Whitf. ('07, pi. 41, fig. 1), U. letsoni Whitf. {ibid. 

 pi. 42, figs. 1-3). I have, fortunately, a number of specimens be- 

 fore me, coming from the same general region as Whitfield's ma- 

 terial ; they were collected for the Carnegie Museum at Hell Creek, 

 Dawson Co., Montana, and show the beak sculpture beautifully in 

 U. retusoides, browni, pyranddatoides, lefsoni, and in addition it is 

 distinctly seen in specimens of TJ. verrucosiformis Whitf. ('07, pi. 

 42, fig. .'';). Some of these fossil forms undoubtedly are the ances- 

 tors of modern species, as is sometimes expi'essed in their names (but 

 not always correctly ; pyramidal oides has nothing to do with Qu. 

 pyramidata, but belongs clearly to the f7'igona-i\]w). Thus it is evi- 

 dent that many North American Unionidse once had radial beak 

 sculpture, and some have preserved fraces of it vp to the present time. 

 This character probably once was more generally distributed, and 

 remains rather well preserved in many old v.'orld forms (and also in 

 South American groups), but in North America it has become more 

 and more obliterated. Such a character, of course, although fit to 

 indicate genetic relationship, is unfit to be used as a principle for 

 classification. 



The structure of the soft parts, which indicates close relationship 

 between Quadrula and Parrcysia, is much more reliable, in fact ac- 

 cording to my experience, is absolutely reliable. In this connection 

 it should be mentioned that in one of our gravid Porreysias only the 

 outer gills were filled with eggs ; but microscopical investigation 

 showed that also the inner gills had the typical structure of the 

 female marsupial gill, and that, in this instance, the specimen was 

 just in the beginning of the period of gravidity, and the inner gills 

 were not yet charged. Similar cases might sometimes lead to mis- 

 takes, if investigated only superficially. 



Of course, we now stand before the task of redefining the sub- 

 family Hyriince according to the South American typical iepresei;<a- 

 tives, and to investigate additional so-called Hyri'ncs from Asia and 



