RHYNCHOPORA 235 



cavity, but is covered by the median portion of the hinge-plate, being 

 open only towards the front, the median septum continues anteriorly from 

 the beak for about one-fourth the length of the valve. 



The fine surface markings are obscure upon all specimens examined, 

 but occasional, rather inconspicuous concentric lines of growth are pres- 

 ent towards the anterior margin. The shell structure is finely punctate. 



Remarks. In general form this species approaches very closely to 

 R. cooperensis, the most conspicuous difference being in its somewhat finer 

 plications, and even in this character it grades into the other. The two 

 forms should perhaps be considered as synonyms, but the only typical 

 representatives of R. persinuata have been found at a somewhat higher 

 geological horizon than the typical R. cooperensis, and the two forms have 

 in consequence been considered as distinct. Furthermore the punctate 

 shell structure has not been actually observed in R. cooperensis. The 

 shell which was described by Miller as Camarophoria occidentalis from Lake 

 Valley, New Mexico, is clearly identical with R. persimiata. Authentic 

 examples of Miller's species from the typical locality exhibit none of 

 the characters of Camarophoria, but they do agree in all respects with 

 authentic specimens of Winchell's species. The punctate structure of the 

 shell is commonly obscure and frequently cannot be detected at all. The 

 type of the species is an internal cast in a rather coarse dolomitic material, 

 which is incapable of preserving such characters, but in one specimen 

 from the Fern Glen formation of St. Louis County, Missouri, the puncta- 

 tion of the shell can be clearly seen on parts of the surface. The speci- 

 men, which exhibits this character best, is one of those from Lake Valley, 

 New Mexico. The internal characters of the rostral portion of the 

 brachial valve have not been observed by sectioning authentic specimens 

 from the typical locality, both because such specimens are too uncommon 

 and because their condition of preservation is not favorable. One excel- 

 lent internal cast of this portion of the shell from the typical locality, 

 clearly shows, however, the presence of the undivided hinge-plate which 

 is characteristic of the genus. The median septum divided posteriorly 

 is also clearly shown in this specimen, but the divisions of the septa seem 

 to give support to the hinge-plate to a point somewhat farther anterior in 

 position than in R. cooperensis, but such a character may be expected to 

 vary even within a single species. 



H orizo-ti. Kinderhook. 



RHYNCHOPORA ? COOPERENSIS (Shumard) 

 Plate XXX, Figs. 7-15 ; ? 22-25 



1855. Rhynchnella Cooperensis Shum., I and II Rep, Geol. Surv. Mo., 



p. 204, pi. C, figs. 4a-d. 



1894. Rhynchonella cooperensis Keyes, Mo. Geol. Surv., vol. 5, p. 101. 

 1910. Rhynchopora f cooperensis Weller, Bull. Geol. Soc. Am., vol. 21, 



p. 515, fig. 18. 



