28 TRANSACTIONS OF THE [1888 



find Belemnitella, Baculites, and Exogyra, nor are their places 

 supplied by closely related genera. On the other hand, how- 

 ever, we do find two Cretaceous fiDrms, the Gryphea vomer and 

 Gryphea vesicularis, extending well up into the Eocene beds. 

 Nevertheless, these two exceptions make but little diiFerence 

 in the totality of the fauna, since they are too restricted in 

 range to effect more than a local change in a small part of the 

 assemblage of specific forms. The first of these species seems 

 to be moderately numerous in the indurated gray-green sands 

 and shell-limestone of the cliffs at Upper Marlboro ; while of 

 the latter, only two or three broken single valves have been 

 found at remote intervals in the ferruginous sands of the cliffs 

 above the railroad bridge leading across the Severn river. 



The middle strata of the Eocene seem to yield the largest 

 and most clearly developed examples of the genus Turritella. 

 Two fine species belonging thereto are occasionally found in 

 almost perfect condition, especially in the vicinity of Matta- 

 woman Creek, and less frequently in the decomposing shell-rock 

 near Upper Marlboro. The Turritella Mortoni is much the 

 more variable of the two, and occasionally specimens are found 

 which measure five inches in length by nearly two inches in 

 width through the basal whorl. Numerous examples of both 

 species have been examined by the writer, and thus far the T. 

 humerosa has always been of a broader form, with heavily 

 carinated whorls and more widely curved base. In general, 

 the proportions of this species have been found to be as three 

 and a half to one, while in a few specimens it has been nearly 

 as three to one. The proportions in T. humerosa have gene- 

 rally appeared much more slender, scarcely more than two and 

 a half to one, while the margins of the whorls were destitute 

 of the high carinate ridges which appear so conspicuous in the 

 former species. In this latter the surface is more even, regu- 

 larly tapering, and only broken by the slender raised lines 

 which wind around the whorls. 



From the foregoing statements it will be perceived that 

 characteristic fossils are not lacking to distinguish the forma- 

 tion throughout all of its accessible exposures on the Western 

 Shore. 



