n6 NORTH AMERICAN INDEX FOSSILS. 



D. Zoarium not belonging to the foregoing 8J. 



8J Zoarium a thin expansion, traversed on both sides by salient ridges or crests 



united into cups XC. Glypiopora. 



8 \ Zoarium free, of four or more vertical leaves radially arranged. 



XCT. Evactinopora. 

 8j Zoarium a subcircular unilaminar expansion with basal epitheca. 



XCIV. Lichenalia. 

 8J Zoarium a thin incrustation, with hexagonal or polygonal apertures. 



XCVII. Paleschara. 

 V. CHILOSTOM ATA. Zocecia of various forms arranged side by side with more or less 

 anterior orifice of smaller diameter than zocecium and closed by a movable cover, 

 appearing often to occupy the whole surface of zoarium owing to non-calcifica- 

 tion of the front wall and its removal in fossilization E. 



e. Bifoliate, mostly free 9j. 



9% Apertures in longitudinal series, oval, and occupying most of the cell sur- 

 face OIL Bijlustra. 



94 Apertures semilunar or crescentic in a large hexagonal area. 



CIV. Onychocella. 



E. Cells on one side only \o\, 



\o% Cells with openings occupying the whole or nearly the whole of the ex- 

 posed surface ; encrusting CV. Menibranipora. 



\o\ Cells with opening only in anterior part ; form bulbous or urn-shaped. 19*. 

 19* Aperture entire, with one or more supplementary pores. 



CVI. Adeonellopsis. 

 19* Apertures notched below, supplemental pores not present. 



CVII. Schizoporella. 



PALAEOZOIC SPECIES. 



Order CTENOSTOMATA Busk. 



I. Rhopalonaria Ulrich. 



Zoarium sunken for about half its mass into the object on which 

 it grows (generally a coral, crinoid stem, or shell) and usually pre- 

 served only as threadlike excavations in the surface of this object, 

 often filled with clay. Zocecia unknown. Ordovicic-Missis- 

 sippian. 



1. R. venosa Ulrich. (Fig. 177, a.) Ordovicic. 

 Consists of delicate fusiform cells connected by slender stolons 



of the average length of the cells ; branching irregular, pinnate or 

 sometimes netlike. Fusiform cells average 0.3 mm. in length by 

 O.I mm. or less in diameter. Excavated in corals, shells, etc. 

 Richmond beds of Ohio and Indiana. 



2. R. attenuata U. and B. Siluric. 

 Fusiform cells shorter and farther apart than in preceding. 

 Niagaran beds of New York and Pennsylvania. 



