BRYOZOA. 463 



CERAMOPORA IMBRICATA Hall. 



f'erainopora imbricata Hall, 1852. Pal. N. Y. Vol. n, p. 169. PI. 40e, flg. la-li. 



Zoarium free, discoidal. plano-convex, under side sometimes 

 slightly concave, from five to fifteen mm. in diameter; thickness 

 at center seldom exceeding four mm., usually only about two 

 or three mm. No epitheca on the lower side. Lower or basal 

 portion of zoarium composed of a cellular or spongy tissue, 

 from which the zocecia grow out more or less obliquely. At the 

 depressed center of the zoarium the zooecia are nearly direct, 

 but toward the margin they gradually become more and more 

 oblique. Zooecia compressed tubular, being long oval in trans- 

 verse section. Apertures imbricating, arranged in multiplying 

 radial series, all facing away from the center, triangular or 

 oval iu outline, 0.5 to 0.7 mm. in their long diameter. Inter- 

 cellular space occupied by irregularly flexuous rows of meso- 

 pores, variously shaped, short. Zooecial tubes and mesopores 

 communicate rather freely by means of perforations in the walls. 

 Besides the Avails have that granular structure which is sup- 

 posed to indicate an originally minutely porous condition. 

 Lunarhmi small, yet well marked. No diaphragms developed. 



The remarkable features about this species are its free habit, 

 and the spongy basal layer. When compared with the other 

 forms which are generally referred to the genus, it does not 

 seem probable that they are congeneric. The Lower Silurian 

 species I refer to either Ceramporella or Crepipora. Several of 

 the Upper Silurian forms which Hall has regarded as congeneric 

 with C. imbricata, are most probably referable to the FISTULI- 

 PORID.E, (Eridopora Or.). The same is believed of Ceramopora 

 huronensis Nich., from the Hamilton formation. 



Position and locality: Niagara group: Lockport, N. Y. (Hall); 

 Osgood, Indiana. 



