HeLDERBERG Foif.MATION IN MARYLAND 21 



by six or seven plications on each side of the mesial lobe and sinus, which 

 are simple from their origin; mesial sinus marked by two plications, with 

 three corresponding ones on the opposite valve (rarely three plications 

 in the sinu?, and four on the corresponding elevation) ; plications crossed 

 by strong imbricating lamellae, which are deeply arched, giving the sur- 

 face a rugose aspect. This species bears a close resemblance to Atnjpa 

 rugosa; but all the specimens examined are nearly uniform in size, and 

 not so large as the larger ones of that species. The plications are also 

 simple from their origin, though marked by imbricating lamelljB much in 

 the same manner." Hall, 1852. 



The shell is often subcircular in outline. In nearly all individuals seen 

 in Maryland the mesial elevation is formed by two plications which 

 coalesce towards the beak, one plication is found in the mesial sinus and 

 three to four plications on each side of the sinus and fold. It has been 

 established that no spirals occur in these shells, hence Schuchert removes 

 this species from among the Atrypas. Its generic position is not assured. 

 This species is abundant in the Tonoloway of Maryland. 



Occurrence. — Helderberg Formatiox, Keyser Member. Pinto, 

 Market Street Bridge and Viaduct Cumberland, Cash Valley. 



Collection. — Maryland Geological Survey. 



Camarotcechia litchfieldensis (Schuchert) 

 Plate LXIII, Figs. 11-14 



Atrypa sp. Hall, 1852, Nat. Hist. N. Y., Pal., vol. ii, p. 330, pi. Ixxiv, figs. 3 



and 12. 

 Rhynchonella agglovierata Weller, 1903, Geol. Survey N. J., Pal., vol. ill, pp. 



234-235, pi. xxi, figs. 5-11. 

 Rhynchonella (?) litchfieldensis Schuchert, 1903, Amer. Geol., vol. xxi, p. 167, 



figs. 



Description. — " Shell subtriangular, usually a little wider than long, 

 the valves subequally convex, the postero-lateral margins tapering to the 

 beak, where they form an angle of about 90° ; the lateral and anterior 

 margins rounded. Pedicle valve most prominent near the umbo, the beak 

 sharply pointed, arched over that of the opposite valve; mesial sinus 

 rather shallow, rounded in the bottom, not extending back to the center 



