MARYLAND GEOLOGICAL SURVEY 221 



each other by angular, irregularly shaped mesopores. Embedded in these 

 walls numerous acanthopores may be noticed. In longitudinal sections 

 the zooecia are provided with rather infrequent complete diaphragms and 

 mesopores with partitions which are four or five times as numerous. 



Occurrence. MARTINSBURG SHALE (Eden division). Abundant and 

 characteristic in the Eden shale of the Ohio Valley. Impressions of a 

 ramose bryozoan in the upper part (Eden) of the Martinsburg shale at 

 Jordans Knob, one and one -half miles northeast from Fort Loudon, 

 Pennsylvania, and Cowans Gap, five miles northeast of McConnellsburg, 

 Pennsylvania, have the external features of this species. * 



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



Family BATOSTO1WELLIDAE 



Genus BYTHOPORA Miller and Dyer 



BYTHOPORA ARCTIPORA (Nicholson) 



Plate LIII, Figs. 11-13 



Ptilodictya f arctipora Nicholson, 1875, Ann. Mag. Nat. Hist., 4th ser., 



vol. xv, p. 180, pi. xiv, figs. 4-4b. 

 Ptilodictya ? arctipora Nicholson, 1875, Pal. Ohio, vol. ii, p. 262, pi. xxv, 



figs. 9-9b. 

 Bythopora arctipora Bassler, 1906, Proc. U. S. Nat. Mus., vol. xxx, p. 90, 



pi. ii, figs. 1, 2. 



Description: This minute species is characterized by its long, slender, 

 cylindrical branches, a millimeter or less in diameter, made up of zocecial 

 tubes which open at the surface in elongate, often attenuate, orifices. 

 The internal structure is that of the genus Bythopora, that is, the zorecial 

 walls are fused in the mature region, diaphragms are practically absent, 

 the apertures are oblique and narrowed above, and the interspaces are 

 canaliculate. Mesopores are present but small, and. on account of the 

 small size and little development of the zocecia in this species, they are 

 inconspicuous. 



Occurrence. MARTINSBURG SHALE (Eden division). An abundant 

 and characteristic Eden fossil of the Ohio Valley. Not so abundant in 



