158 NORTH AMERICAN INDEX FOSSILS. 



polygonal or circular vestibules and numerous small mesopores, 

 which often completely surround the zooecia. 

 Stones River and Black River of Minnesota. 



LXXVIII. Intrapora Hall. 

 Ramose from a spreading base with compressed and dichoto- 

 mously divided branches; zooecia on both sides, tubular, at first 

 parallel to mesotheca, then bending abruptly outward ; apertures 

 oval, with peristome ; minute angular pits, the openings of tabu- 

 lated mesopores, in the interspaces, sometimes closed by calcareous 

 tissue. Dev.-Miss. 



135. I. puteolata Hall. Devonic. 

 Flattened, dichotomously branching frond, from spreading base ; 



width usually 2 to 4 mm. but sometimes 20 mm. or more; oval 

 apertures closely and irregularly disposed, frequently in contact, 

 with strong peristomes, interspaces and margins with angular pits 

 or mesopores. 



Hamilton of Falls of the Ohio. 



LXXIX. Coscinella Hall. 

 Explanate fronds of anastomosing branches from spreading 

 base ; zooecia on both sides of frond, tubular, resting upon the 

 mesotheca, with rather long direct vestibules and irregularly dis- 

 posed circular apertures ; spaces between vestibules and margins 

 of fenestrules occupied by numerous tabulated mesopores which 

 open on the surface as fine pits. Dev. 



136. C. elegantula Hall and Simpson. Devonic. 

 Fenestrules irregular in form, size and distribution ; apertures 



circular, with pronounced peristomes, generally separated by a 

 single series of mesopores only. 

 Hamilton of Ontario. 



LXXX. Rhinidictya Ulrich. 

 Bifoliate ramose, of narrow compressed bifurcating straight- 

 edged branches with parallel margins, attached by continuous ex- 

 panded base; apertures between longitudinal, slightly elevated or 

 flexuous ridges, carrying a crowded row of small blunt spines ; 

 space around apertures sloping to summit of ridges. Ordovicic. 



137. R. mutabilis Ulrich. (Fig. 208, i.) Ordovicic. 

 Branches commonly from 2.3 to 3.2 mm. wide, dividing at inter- 

 vals of from 7 to 16 mm.; non-celluliferous margins often almost 



