303 Systematic Paleontology 



Surface very finely and evenly striated. This species bears some resem- 

 blance to 0. [Dalmanella] elegantida of the Niagara gronp ; but it is more 

 finely and beautifully striated, the dorsal valve is more gibbous, .... 

 and the beak less arched." Hall, 1859. 



Certain individuals referred to this species are much more circular in 

 outline than the forms described by Hall, the cardinal angles being less 

 extended and the valves less elongate. 



Concerning this species Schuchert remarks that it " is easily confounded 

 with Dalmanella perelegans, but it is always smaller, more obese, and 

 with finer striae. Hall states that these specimens are from the " shaly 

 limestone of Cumberland, but is in error, since all those now found are 

 from the Keyser member, and none have been seen in the Xew Scotland 

 member." 



Occurrence. — Heldeebeeg Formation, Ke.yskr Member. Keyser, 

 West Virginia; Cash Valley, Devil's Backbone, Market Street Bridge, 

 Cumberland, section southwest of Eawlings, Pinto, Viaduct Cumberland, 

 Tonoloway, Maryland ; Pleasant Valley, Bedford County, and Hyndman, 

 Pennsylvania. 



Collection. — Maryland Geological Survey. 



[Maynard.] 



Genus RHIPIDOMELLA CEhlert> 



Ehipidomella emarginata (Hall) 

 Plate LV, Figs. 1-8 



Ortliis oblata var. emarginata Hall, 1859, Nat. Hist. N. Y., Pal., vol. ill, p. 

 164, pi. xa, figs. 4-6, 1861. 



Description. — " Among the collections from the Lower Helderberg 

 rocks of Cumberland, Maryland, there are numerous specimens of an 

 Ortliis, having the same general characters as 0. ollata, but proportionally 

 narrower and the beak more extended. The dorsal valve is very convex, and 

 the ventral valve is marked by an undefined depression, which, beginning 

 below the beak, gradually becomes wider and deeper, producing a deep 

 sinuosity or emargination in front. 



• See Hall and Clarke, 1892, Nat. Hist. N. Y., Pal., vol. vili, pt. 1, p. 209. 



