white.] ANNOTATED CATALOGUE. 51 



Alb. & Mart.; and the other two are referred provisionally to Pupilla 

 Leach. All three of these forms are represented on Plate 20. Owing 

 to the imperfection of the type specimens of these three species, their 

 reference to the subgenera which have just been mentioned is not made 

 with entire confidence; but whether this reference is correct or not, it 

 is a well-established fact that the family Pupidse had acquired, as early, 

 at least, as the earliest Eocene, nearly or quite all the characteristics 

 which distinguish it at the present day. 



6VCCTSU>M. 



Although so large a number and great variety of other land-snails 

 have been discovered in the strata of various geological periods, only a 

 single species referable to the Succinidse has yet been found in North 

 Americau strata. This is succinea papiUispira, White,* which was ob- 

 tained from the upper portion of the Green Eiver Eocene group in 

 Southern Wyoming, and which plainly belongs to the subgenus 

 Bracliyspira Pfeiffer. 



NERITHME. 



Since the greater part of the known species of this family, both living 

 and fossil, are of marine origin, only those of its fossil representatives 

 which are found associated with such forms as indicate that they lived in 

 a brackish or nearly fresh water habitat will be considered in this article. 

 The species thus falling under consideration embrace two subordinate 

 types of Neritina and these only. One of the types is apparently iden- 

 tical with that of the common fmvatile living species of Neritina, which 

 may be regarded as the typical section of the genus,t but the other type 

 is extinct. Instead of having been confined to either brackish or fresh 

 water, both these types have representatives in strata of both brackish 

 water and marine origin. That is, for example, a species of each type 

 is found iu the Laramie group, associated with Corbicida, Corbula, Unto, 

 and Melanin. Other species of both types are found in Cretaceous 

 strata, associated with such unmistakably marine forms as the Aviculi- 

 dse, Arcidae, Turritellidse, &c. 



The earliest species referable to this family which is at present known, 

 and which comes within the scope of this article, is Neritina nebrascensis, 

 Meek & Hayden,| which was found iu the vicinity of the Black Hills, 

 in strata believed by those authors to be of Jurassic age. It is plainly 

 a true Neritina, but those authors found it associated with species that 

 are regarded as indicating a purely fresh- water habitat, namely, Unio, 

 Viviparus, Lioplacodes, &c. It is represented on Plate 3. 



*An. Rep. U. S. Geol. Sur. Terr., for 1878, Part I, p. 45, pi. 19, fig. 4. 



t The Laramie species, N. volvilincata, shows a faint crenulation of the border of the 

 inner lip; and some small examples, apparently the young of this species, lately dis- 

 covered, show a distinct denticulation of that border. Perhaps this species ought to 

 be referred to Neriia, but for the present I leave it with Neritina. 



{Paleoutology of the Upper Missouri, p. 109. 



