322 THE PALEONTOLOGY OF MINNESOTA. 



[Creptpora. 



Genus CREPIPORA, Ulrich. 



Crepipora, ULRICH, 1882, Jour. Cin. Soc. Nat. Hist., vol. v, p. 157; 1890, Geol. Surv. 111., vol. viii, 



pp. 380, 469. 



Zoaria incrusting, massive, or hemispherical; in one case forming regular hollow 

 branches. Surface, especially in the first and last styles of growth, exhibiting at 

 regular intervals maculae of mesopores, appearing as minutely porous or subsolid 

 elevations or depressions. In the massive forms these maculae, to which the meso- 

 pores are usually restricted, are very small. Zocecial tubes erect, their apertures 

 very slightly oblique and varying from rhomboidal to subpyriform in shape. Luna- 

 rium small and easily overlooked except in well preserved examples; best shown in 

 tangential sections. Thin diaphragms are developed in moderate numbers. 



Type : C. simulans Ulrich. 



Eleven or twelve species, several as yet undescribed, are known to me having 

 the characters ascribed to this genus. Three of these are Trenton, the rest, save an 

 Upper Silurian species from Gotland, are Utica or Hudson Eiver group forms. 



Crepipora differs from Ceramporella in having much fewer mesopores (typically 

 none) in the inter-macular spaces, longer tubes, and less oblique apertures. C. epi- 

 dermata Ulrich, from the Hudson River group of Illinois, is closely related to the new 

 genus Bythotrypa, and ought perhaps to be referred to that genus, but it has seemed 

 the wiser course to leave the species as originally described until special investiga- 

 tions into the inter-relations of the Ceramoporidce can be taken up. 



CKEPIPOKA SUB^EQUATA, n. sp. 



PLATE XXVIII, FIGS. 26-28. 



Zoarium a small laminar or incrusting expansion, 1 to 3 mm. thick. Zocecial 

 apertures approximately direct, angular, often quadrate or pentagonal, of nearly 

 uniform sizes on all parts of the surface, no distinguishable clusters of cells larger 

 than the average having been developed; ten in 3 mm. Lunarium very slightly 

 developed, the zocecial apertures and walls appearing much more like those of 

 species of Monotrypa than of a ceramoporoid. Tangential sections, however, (see figs. 

 26 and 27) afford more or less clear evidence of its presence, but it is rare to find 

 more than one of the ends of the lunarium projecting inward from the wall. Many 

 of the angles of junction are thickened and include an acanthopore-like structure. 



