WHITE.] ANNOTATED CATALOGUE. 433 



The shells of both these large species are strong and massive, and 

 both have strong and well developed cardinal and lateral teeth, such as 

 are observable upon the shells of the large living river Uniones. 



The other species of Unto that have been obtained from the Black 

 Buttes locality have all been described by me under the following 

 names respectively: Unio propheticus, U. brachyopisthus, U. proavitus, 

 U. aldricMj (7. goniambonatus, U. holmesianus, and a form which I have 

 doubtfully referred to the U. dance of Meek & Hayden * has also been 

 obtained there. These seven species are represented by appropriate 

 figures upon Plates 13, 15, 16, and 19. They cannot fail to be especially 

 interesting to those who are familiar with the UnioDe fauna of the 

 Mississippi drainage system. 



The form which is represented by figures 1 and 2, on Plate 18, has 

 already been referred to as having been doubtfully identified with 

 Unio dance, the type specimens of which species were obtained by Meek 

 & Hayden from the Judith River beds of the Upper Missouri Eiver 

 region. It is not improbable that further comparison will make it 

 necessary to regard the Black Buttes form as a distinct species. 



In some respects, at least, the most interesting of these fossil species 

 of Unio is U. holmesianus White. It is especially noteworthy as indi- 

 cating, in connection with its associates, the wide diversity of subordi- 

 nate types that the genus Unio had attained in the Laramie period, and 

 also as affording a fine fossil example of one of the most characteristic 

 subordinate types of Unio that are now peculiar to North American 

 fiuvatile waters. 



Unio gonionotus White t is illustrated on Plate 13. It was discov- 

 ered, by Professor Powell, in the Laramie strata of Southern Utah, 

 where alone any specimens of the species have yet been found. It is 

 an interesting form, especially because of the strong plications which 

 it bears, and which are similar to those that characterize various living 

 species, and 'also .because it possesses the excessively shortened front 

 which has before been noticed as characterizing other fossil Uniones. 



Only one other species of Unio, which is referred to tne Laramie 

 Group, remains to be noticed by name in this article j but, judging 

 from various fragments that have been found at different localities, it is 

 quite certain that several, perhaps many, other species exist there. In- 

 deed, the known wide diversity of type that the genus Unio had attained 

 during the Laramie period seems necessarily to imply that a greater num- 

 ber of specific forms then existed than have yet been discovered. 



The species last referred to, and which is illustrated on Plate 18, 1 

 have described under the name of Unio mendax.% Specimens of it 



* For original descriptions and figures of these seven forms see An. Rep. U. S. Geol. 

 Sur. Terr, for 1878, Part I, pp. 62-68, pi. -2-2, 26, 27, and 29. 

 t An. Rep. U. S. Geol. Sur. Terr, for 1878, Part I, p. 71, pi. 26, fig. 2. 

 tBull. U. S. Geol. Sur. Terr., vol. iii, p. 605. 

 28 G 



