THE NAUTILUS. 141 



Wyoming ; or at the beak sculi)ture of a number of species described 

 by "Whitfield from the Laramie of Montana (see : Bull. Amer. Mus., 

 N. H. 19, '03 p. 483 and 23, '07 p. 628), we cannot deny, that we 

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

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

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

 fig. 3), JJ. percorrvgalus 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, broicni, pyrainidaloides, lefsoni, and in addition it is 

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

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

 tors of modern species, as is sometimes expressed in their names (but 

 not always covreclly ; pyramidaloides has nothing to do with Qu. 

 pyramidata, but belongs clearly to the <?-/(/o?2o-type). Thus it is evi- 

 dent that many North American Unionidse once hud radial beak 

 sculpture, and some have preserved traces of it up 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 relationshij), is unfit to be used as a principle for 

 classification. 



The structure of the soft parts, which indicates close relationship 

 between Quadrula and Parreysia, 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 Parreysias 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 s|)ecinien 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 Hyriincc according to the .South American ty])ical representa- 

 tives, and to investigate additional so-called Hyriince from Asia and 



