316 SYSTEMATIC PALEONTOLOGY 



Genus CYCLORA Hall 



CYCLOEA MINUTA Hall 



Plate L, Figs. 23-26 ; Plate LJI, Figs. 10-12 



Cyclora minuta Hall, 1845, Amer. Jour. Sci. and Arts, vol. xlviii, p. 294. 

 Holopea nana Meek, 1871, Proc. Acad. Nat. Sci. Phila., p. 172. 

 Cyclora minuta Meek, 1873, Geol. Surv. Ohio, Pal., vol. i, p. 152, pi. xiii, 

 figs. 7a-e. 



Description. Shell small, averaging 1.00 mm. in height, smooth, con- 

 sisting of about three volutions which rapidly expand toward the mouth 

 and form a moderately elevated spire. The upper two whorls are quite 

 small and the shell is formed in large part by the third whorl. The 

 aperture is round and well defined. 



This interesting minute species occurs literally by the million at certain 

 Middle and Upper Ordovician horizons where usually all the associated 

 shells are similar dwarfed or embryonic forms. Cyclora minuta possibly 

 represents the very young stages of Cyclonema or Stropliostylus, althougn 

 its black corneous shell substance is quite different from either of these 

 genera. Probably a closer assumption would be to consider them as 

 embryonic forms of Holopea. The latter genus, however, is sparsely 

 represented by individuals in the rocks in which Cyclora abounds. 



Common at many horizons and localities of the Mohawkian and Cin- 

 cinnatian in the United States and Canada. In the Cumberland Valley, 

 however, it has been found only in the lower portions of the Martinsburg 

 shale, particularly in the Sinuites zone at the base. 



Occurrence. MARTINSBURG SHALE (Sinuites and Corynoides beds). 

 Chambersburg, Pennsylvania; Williamsport, Maryland and Strasburg, 

 Virginia. 



Collections. Maryland Geological Survey, U. S. National Museum. 



CYCLORA PARVULA (Hall) 

 Plate L, Figs. 28-30 



Turbo f parvulus Hall, 1845, Amer. Jour. Sci. and Arts, vol. xlviii, p. 294. 

 Cyclora ? parvula Meek, 1893, Geol. Surv. Ohio, Pal., vol. i, p. 154. 



Description. " Spire elevated, volutions about four, smooth ; first 

 whorl angulated upon the center towards the aperture ; outer edge of the 



