white. 1 ANNOTATED CATALOGUE. 59 



Although the genus Goniobasis has not been recognized in any of the 

 strata of North America of later age than the Eocene, it cannot be 

 doubted that it existed somewhere during the later epochs; probably in 

 some of the streams which have since become upper branches of the 

 Mississippi Eiver system, where it is now abundant. 



In the Miocene freshwater deposit, which has been several times re- 

 ferred to as occurring in Southern Idaho and Northern Nevada, called 

 the Truckee Group by King, no species of the genus Goniobasis have 

 been recognzrd; but Mr. Gabb obtained a shell which he referred to 

 Lithaaia (a genus which is regarded as a member of the Ceriphasiidse), 

 and described it under the name of L. antiqua.* It is illustrated on 

 Plate 32. 



RISSOHXE. 



The Bissoidee, in consequence of their small size and comparative 

 rarity, form an inconspicuous feature of the non-marine fossil fauna? which 

 are discussed in this articie; and yet they are interesting because they 

 show that as early at least as the close of Mesozoic time several genera 

 of that family inhabited the then existing fresh and brackish waters ; and 

 that the most of those which have been discovered are either congeneric 

 with existing forms, or so closely like them, that we cannot properly do 

 otherwise than refer them to existing genera, although we may enter- 

 tain some doubt as to their real affinities. Up to the present time eight 

 fossil species have been published and referred to this family, most of 

 which were obtained from the Laramie Group. 



Among these the two living genera Hydrobia and Bythinella are re- 

 cognized, and also one new genus, Micropyrgus, which was proposed by 

 Mr. Meek.t 



Four species, Hydrobia subconica, H. anthonyi, H. eulimoides, and H. 

 warrenana, were described from the Laramie strata of the Upper Mis- 

 souri Eiver region by Meek & Haydeu.J The first one comes from the 

 Judith Eiver beds, and the other three from the Fort Union beds. They 

 are all illustrated on Plate 27. Except in the case of H. anthonyi, 

 those authors express some doubt as to the true generic relations 

 of these shells with Hydrobia, and reason for similar doubt seems to 

 exist in relation to that species also. For present convenience, how- 

 ever, all four of these forms are left under Hydrobia, where those authors 

 placed them. 



The Fort Union Laramie beds also furnished Meek & Hayden with 

 the types of their Micropyrgus mihutulus,§ which they referred to the 

 Eissoidae. It is represented by copies of Mr. Meek's figures on Plate 26. 



'Paleontology of California, vol. ii, p. 13, fig. 22. 

 tU. S. Geol. Sur. Terr., vol. ix, p. 574. 



I For figures and descriptions of these four species, see TJ. S. Geol. Sur. Terr., vol. 

 ix, pp. 571-573, pi. 43. 



$ U. S. Geol. Sur. Terr., vol. ix, p. 575, pi. 43, fig. 18. 



