3io 



NORTH AMERICAN INDEX FOSSILS. 



313. A. rugosa Hall (Fig. 388.) Siluric. 



Smaller than A. nodostnata and with equally convex valves. 

 Surface marked by strong sinus andjfold and concentric rugose 

 ^^ _^_ lamellae and by plications which 



are less rounded than in A. no- 

 do striata. 



Niagaran of New York, Ken- 

 tucky, Indiana, Anticosti. 



\'\ 314- A. reticularis (Linnaeus). 



(Figs. 389, a; 389, b; 392, 

 a-c.) Siluric and Devonic. 

 Pedicle valve often nearly 

 flat. Surface reticulated by the radiating and concentric striae. 

 A characteristic Siluric and Devonic fossil throughout the world. 



a 



FlG. 388. Atrypa rugosa, 

 enlarged (Pal. N. Y. II.). 



with strice 



Fig. 



Atrypa reticularis (Helderbergian) (Pal. N. Y. III.). 



tlG. 389, b. Atrypa reticularis (Onondaga) (Pal. N. Y. IV.). 



315. A. impressa Hall. (Fig. 390.) Devonic. 



Differs from A. reticularis in being more gibbous, in the absence 

 of a sinus in the pedicle valve and in the depression of the brachial 

 valve toward the front. The striae are finer and less conspicuous. 



Schoharie of New York, Michigan. 



