Maryland Geological Survey 547 



sometimes involute ; posterior dorsal margins often alate or auriculate ; 

 external surface most commonly undulated concentrically, rarely smooth 

 or radially or reticulately sculptured ; ligament external, multivincular, 

 amphidetic, lodged in a long series of similar cartilage pits placed trans- 

 verse to the cardinal margin ; hinge edentulous ; form monomyarian in the 

 adult state, the single large muscle impression suhmedial in position; pal- 

 lial line entire. 



There is no genus, perhaps, which is more closely identified with the 

 Cretaceous faunas as a whole than Inoceramus. Although it was initiated 

 in the Jurassic, the spectacular culmination of the group did not occur 

 until well along in the Cretaceous, and the close of the Cretaceous appa- 

 rently marked its extinction. The Inocerami seem to be peculiarly sus- 

 ceptible to changes in environment, and for that reason lend themselves 

 remarkably well to phylogenetic studies, and a mass of detailed work has 

 been done both in England and on the continent upon the genetic rela- 

 tionships of the component species. Their greatest disadvantage as a 

 horizon marker is the fact that for the most part they are so difficult to 

 determine with assurance. 



Inoceramus confertim-annulatus Eoemer 



Inoceramus confertim-annulatus Roemer, 1849, Texas, p. 402. 



Inoceramus confertim-annulatus Roemer, 1852, Kreidebildungen von Texas, 

 p. 59, taf. vii, fig. 4. 



Inoceramus confertim-annulatus Conrad, 1857, Rept. U. S. and Mex. Boun- 

 dary Survey, vol. i, pt. 2, p. 151, pi. v, fig. 5. 



Inoceramus barabini Whitfield, 1885, Mon. U. S. Geol. Survey, vol. ix, p. 75, 

 pi. xv. figs. 3-5. (Not I. barabini Morton.) 



Inoceramus confertim-annulatus Weller, 1907, Geol. Survey of New Jersey, 

 Pal., vol. iv, p. 427, pi. xxxix, figs. 2-5. 



Description. — " Testa transversa, ovata, depressa, concentrice undulato- 

 plicata et striata ; plicis regularibus rotundatis confertis ; intervallis 

 latitudinem plica rum vix aequantibus ; lineis elevatis tenuissimis, aequidis- 

 tantibus, regularibus, et plicas et intervalla ornantibus." — Roemer, 1852. 



Type Locality. — New Braunfels, Texas. 



Inocerami are for the most part so difficult to determine, even from the 

 perfect specimens, that it seems a little audacious to attempt to identify a 



