white.] PALEONTOLOGY — CRETACEOUS FOSSILS. 307 



a Cretaceous bed, associated with TJnio, Cardium, Inoceramm, Anomia, 

 Xeritiiia, and other marine and fresh-water shells." 



Although this interesting locality has been twice visited by myself 

 since Mr. Meek made his collections there, it was found impracticable to 

 make any further collections on account of the discontinuance of mining- 

 operations there and the consequent falling-in of the excavated strata. 

 Mr. Meek found tbem to contain a remarkable assemblage of marine, 

 brackish-water, and fresh- water forms belonging to the following genera : 

 Inocemmus, Unio, Cardium, Cyrena, Anomia, Physa, Valvata, Neriiina, 

 Melampus, Eulima [Eulimellaf], and Turritella. A remarkable feature 

 in this assemblage of fossils is the modern type of the fresh- and brackish- 

 water forms, especially of the Pulmonate Gasteropoda, although they are 

 certainly of Cretaceous age, and probably not much above the middle 

 of the full Cretaceous series as developed in Western North America. 

 The marine character of the Cretaceous strata above these fresh- and 

 brackish-water forms is as well marked as that of those below them. 

 The following are remarks by Mr. Meek (loc. cit. p. 445) in relation to 

 the geological position and affinities of these interesting fossils, the 

 remainder of which it is hoped will be illustrated in a subsequent paper: 



"Here we have from beds certainly overlaid by more than 1,000 feet 

 of strata, containing Cretaceous types of fossils, a little group of forms 

 presenting such modern affinities that, if placed before any paleontolo- 

 gist unacquainted with the facts, they would be at once referred to the 

 Tertiary. Such examples as this illustrate the difficulties with which 

 the paleontologist sometimes has to contend, and show how very cautions 

 we should be in deciding from the affinities of new species of fresh- and 

 brackish- water types of shells (the vertical range of which is unknown) 

 the geological age of the rocks in which they are found ; because species 

 of this kind, from rocks of various ages, often closely resemble each 

 other, while they rarely present such well-marked distinctive features as 

 we see in marine shells from different horizons. Some of the species of 

 Physa, Gyrena, Neritina, &c, for instance, from the clays under consid- 

 eration, closely resemble existing species, while one or two of Melampus 

 present but very slight differences from Paris Basin Tertiary species 

 figured by Deshayes under the name Auricula. 



u It would appear that the indurated clay containing these mixed types 

 of shells must have been deposited, in the form of fine mud, in an estuary, 

 or possibly a larger body of salt water, into which the fresh- water shells 

 were swept by streams flowing in from adjacent land." 



This species, Physa carletoni Meek, is so nearly synonymous with 

 Physa carltonii Lea as to deserve notice. The former was published 

 (loc. cit.) in 1873, and the latter originally in Proc. Acad. Nat. Sci. 

 Phila. p. 125, 1869, and subsequently in Lea's "Observations on the 

 Genus ITnio," vol. xiii, p. 67, pi. 21, fig. 19. The difference of the presence 

 of the letter "e" in the former case is held to be sufficient to destroy its 

 synonymy with the latter $ besides which the two species are clearly dis- 

 tinct, and the names were given in honor, respectively, of two different 

 persons. 



Physa ? 



Plate 7, fig. 13 a. 



From a stratum about 800 feet below that from which the foregoing 

 species of Physa was collected by Mr. Meek, and at a locality about two 

 miles distant, I discovered the example represented on plate 7, fig. 13 a. 

 It is an imperfect cast in sandstone, and was found associated with forms 



