Maryland Geological Survey 169 



Riiipido:mella cyclas Hall ( ?) 

 Plate XIV, Fig. 10 



Orthis cyclas Hall. 18(i0, Thirteenth Rep. N. Y. State Cab. Nat. Hist., p. 78. 

 Orthis cyclas Hall, 1867, Pai. N. Y., vol. iv, p. 52, pi. vii, figs. 2, 3. 

 Rtiipiclomella cyclas Hall and Clarke, 1892, Pal. N. Y., vol. viii, pt. i, p. 225. 

 Rhipidomella cyclas Schuchert, 1897, Bull. U. S. Geol. Surv., No. 87, p. 348. 



Description. — Shell rather praall, transversely subelliptical to siib- 

 quadrate, the specimens from Ernstville, Md., are subelliptical while those 

 from Hanging Eock, W. Va., are more quadrate in outline. Valves rather 

 flat with greatest gibbosity near the umbo; cardinal line about one-half 

 the greatest widtli of the shell. Surface marked by strong and prominent 

 striae which increase both by bifurcation and implantation, and one speci- 

 men shows fine thread-like concentric striae which are thickest toward 

 the front of the shell. Shell structure strongly and finely punctate. 



But few specimens of this form were found in Maryland and West 

 Virginia and they are doubtfully referred to this species. On account of 

 the size, prominent striae and some other characters the specimens from 

 Hanging Rock, West Virginia, were at first referred to this species with a 

 query. The specimens from Ernstville, Md., are broader than Rhipi- 

 domella vamixemi Hall, which they resemble somewhat, a character which 

 appears to be constant and not produced by pressure. Dr. Clarke after 

 examining the specimens said " they are perhaps R. vanuxemi distorted 

 by pressure, still the breadth appears to be constant and perhaps they are 

 entitled to be called a new species." The Ernstville specimens were sub- 

 mitted to Prof. Schuchert, who wrote me " I think they are Rhipidomella 

 cyclas Hall. If your other specimens have a long hinge-line, or at least 

 longer than R. vanuxemi, they are R. cyclas." The specimen from Wil- 

 liams Road which is figured was examined by Dr. J. M. Clarke, who said 

 that " it is as good a Rhipidomella cyclas as any of the New York 

 Hamilton specimens. It is not ]\;nown. however, what this species is and 

 perhaps it is only the young fonn of R. vanuxemi." The figured speci- 

 mens from Ernstville and Williams Road, Md., and from Hanging Rock, 

 W. Va., were also examined by Dr. Grabau, who agreed in comparing them 

 with R. cyclas. As already stated the author is not confident of the 



