l62 



NORTH AMERICAN INDEX FOSSILS. 



150. C. latum Ul rich. (Fig. 214, d.) Mississippian. 

 Branches wider than in preceding (4-5 mm.); cell apertures ele- 

 vated and disposed in diagonal lines. 



Burlington of Illinois and Iowa. 



LXXXVII. Acrogenia Hall. 



Segmented, arising from cylindrical rootlets, two segments from 

 truncated ends of preceding one, each obconical and striated at 

 the base, later becoming flat- 

 tened and bearing apertures in 

 linear series, separated by ridges, 

 largest in marginal row; lunarium 

 prominent. Dev. 



151. A. prolifera Hall. (Fig. 

 213.) Devonic. 

 Apertures small and circular, 



with weak peristomes, and in 

 rows, separated by continuous 

 longitudinal ridges. 



Hamilton of Central and West- 

 ern New York. 



LXXXVIII. Pkismopora Hall. 

 Ramose, of triangular bifurcat- 

 ing or trifurcating branches, 

 sometimes anastomosing and 

 forming clumps; faces subequal, 

 usually slightly concave, edges 



sharp, serrated, or wavy ; the zo- f rond ' X *J and W ™f f ' a f ment en " 

 r ' ' Ji larged, X6. (After Hall and Simpson.) 



oecia arising from mesothecae 



which radiate from center to margins ; apertures sometimes on 

 summit of small papillae ; interzocecial spaces vesiculate, often solid 

 on the surface. Dev.-Carb. 



152. P. triquetra Hall. Devonic. 

 Faces of branches from 3 to 6 mm. wide, concave, the apertures 



in diagonal transverse rows from center of face ; peristomes promi- 

 nent posteriorly ; relatively wide non-celluliferous margins; bifur- 

 cating branches frequent. 



Hamilton of Falls of the Ohio. 



a b 



Fig. 213. Acrogenia prolifera; {a) 



