204 PALEONTOLOGY OF NEW YORK. 



the Upper Devonian of Iowa ;* R. Missouriensis, Shuniard, and R. striato-costata. 

 Meek and Worthen, of the Choteau limestone ; R. explaiiata, McChesney, of the 

 Chester limestone ; R. mutata. Hall, R. Ottumwa, White, of the St. Louis group ; 

 R. Uta, Marcou, R. Eatoniiformis, McChesney, and the Camarophoria Swalloviana, 

 Shumard, of the Upper Carboniferous limestone. 



Shells of this type of exterior abound in all later palaeozoic faunas. 



Genus EAT ONI A, Hall. 1857. 



PLATE LXI. 



1841. Atrypa, Conkad. Ann. Rept. Palffiont. Dept. N. Y. Geol. Survey., p. 56. 



1S42. Atrypa, Vanuxem. Geology of N. Y. ; Rept. Thinl Dist., pp. 120, 121, tigs. 4. 5. 



1S4B. Atrypa, M.vniEit. Geology of N. Y. ; Rept. Fir.st Dist., p. 842, fig. 3 ; p. 343, tig.s. 3, 4. 



1843. Atrypa. Hall. Geology of N. Y. ; Rejit. Fourth Dist., )). 148, tig. 3. 



1857. Eatonia, Hall. Tenth Ann. Rept. N. Y. State Cab. Nat. Hist., pp. 90-92, figs. 1-7. 



1859. Eatonia, Hall. Twelfth Ann. Rept. N. Y. State Cab. Nat. Hist., pp. 35-37, figs. 1-7. 



1859. Eatonia, Hall. PaK-Eontology of N. Y., vol. iii, pp. 241-243, 432-438, pi. xxxvii, figs. 1 a-y, 



2 a-c; pi. xxxviii, figs. 14-26; pi. ci, figs. 1, 2; pi. ci a, figs. 2-6. 



1868. Eatonia, Meek and Woethen. Geol. Surv. Illinois, vol. iii, p. 396, pi. viii, figs. 2 a-d. 



Concavo-convex shells with median fold and sinus, and plicated or radiate- 

 lineate exterior. Anterior margin deeply sinuate. From the beak of the 

 pedicle-valve diverge two lateral cardinal ridges which limit a more or less 

 distinct false area. On the interior the teeth are adnascent to the lateral walls 



*The Rhynvhonella alta, Calvin, which some American writers have considered equivalent to R, pug- 

 nus, Martin, is a local form retaining quite pertistently the features of li. anisodonta, Phillips {R. pugniis, 

 var. anhodonta, Davidson). Though always smaller than the representatives of R. pugiius, occurring in 

 the High Point (New York) fauna, at the base of the Chemung series, it less frequently shows a tendency 

 toward the acute acnminataAWe: fold than the latter. The fact that the New York shell evinces gradations 

 in form which include both the pugmut and the axyiLminata type of exterior is but a further substantiation of 

 the ai'gument upon which McCoy, in 1852, reduced the latter to a variety of the former. This position has 

 been contested by Davidson and other writers, who nevertheless note the great variability of the shells 

 passing under these two names. That it may be convenient to retain both terms is undoubtedly true, but 

 the passage of one sei-ies of forms into the other is quite as apparent among the Devonian as among the 

 Carboniferous shells. It may be a fair question whethev the Devonian shells passing as R. pugnus and R. 

 acuminata are entitled to these names ; whether, for instance, it would not be better to retain Phillip's 

 name, R. anisodonta, for the former, and, possibly, R. triangularis, Sowerby, for the latter. In both of the 

 former cases the originals were from the Caiboniferous limestone of Derbyshire and attained, as a usual 

 habit, a much greater size than the Devonian shells. The American Carboniferous shells representing the 

 specific type o( U. pugnus, namely, R. striato-costata. Meek and Worthen, R. Missouriensis, Shumard, bear 

 a tine radiate-lineate ornamentation, and what might be interpreted as a similar character is apparent in 

 many of Davidso.\'s figures of the Carboniferous species (Carboniferous Brachiopoda, pi. 22), though this 

 feature is not mentioned in his descriptions. The same character is highly developed in the Devonian species, 

 R. Meyendorfi, de Verne uil, a sharply acuminate shell without plications. 



