348 Systematic Paleontology 



Dimensions of the largest specimen are : Lengtli 15 mm. : width 18 mm. 

 Of a smaller specimen : Length 12 mm. ; width 13 mm. 



In general this species much reminds one of Rhynchotreta cimeata of 

 the Silurian, and is apparently related to it. It is true that the ventral 

 beak is not so erect nor high, nor is the shallow sinus in the posterior 

 region of the dorsal valve so well developed as in the Silurian species, yet 

 the general characters of this Devonian shell are so similar that for the 

 present R. cumherlandica is best referred to Khynchotreta. In young 

 specimens the R. cuneata aspect is most marked. In the Konieprussian 

 of Bohemia undoubted Ehynchotreta occurs in R. nympha Barrande. 



The rectangular posterior margins of R. cumherlandica distinguish it 

 from all associated rhynchonelloids. 



•Weller has recently described a form of this genus as R. transversa^ 

 from the higher Coeymans zone of New Jersey. This form is readily 

 distinguished from R. cumherlandica by its much smaller size, fewer pli- 

 cations, and especially because the dorsal fold has but two plications, M'hile 

 in the Maryland species there are always three or four. 



Occurrence. — Oriskaxy Formation, Ridgely Member. Knobly 

 Mountain near Cumberland, Maryland ; Queen's Point, opposite Keyser, 

 West Virginia ; Warren Point, Pennsylvania. 



Collections. — Maryland Geological Survey, U. S. National ]\Iuseum. 



[Rowe.] 



Genus STENOCHISMA Conrad = 

 This genus as now understood differs from Camarotarliia in that "the 

 septum of the dorsal valve is represented only by an exceedingly obscure 

 median thickening, being in fact virtually wanting." In other words, 

 there is no subcardinal cavity as in Camarotaichia, "bat the hinge-plate 

 is divided by a fissure which extends to the bottom of the shell, and con- 

 tains a slender longitudinal cardinal process." 



' Weller, 1903, Geol. Surv. N. J., Pal., vol. iii, p. 286, pi. xxix, figs. 32-39. 

 = For generic description, see Hall and Clarke, 1893, Nat. Hist. N. Y., Pal., 

 vol. viii, pt. il, p. 187. 



