PLATE I.V— Continaed. 



Atkypa aspera, Schlothoiin, v;ir. occidentalis, Hall. 



Flga, 18. 10. DonuU and pi-otile views of a Devonian shell ; showings the gibbosity of the brachial valve, the 



coarse plications and strong concentric lainellte. 

 Fijr. 20. A preparation of the brachidinm exposed by the I'emoval of the jiedicle- valve ; showing the form 



of the cones and loop. (Whitfield ) 



Upper Devonian. Ind^eadence, Iowa. 



Athypa spinosa, Hall. 



Fig. 21. The exterior of the i>edicle-valve ; showing the extension of the concentric lamellte into well- 

 defined spinules. When these spinides are removed such shells present coai-se, strong plications 

 like those of A. aipera. 



Hamilton group. Moscou), N. Y. 

 Kig. 22. Dorsal view of a siieciraen with longer spines. A poi-tion of the brachial valve has been removed, 

 showing one of the spii-al cones, which is con.'^iderably depre-ised. 

 Hamilton gi-oup. Canandaigtui Lake, N. Y. 



Atrypa hystrix, Hiill. 



Fig. 38. The exterior of a pedicle-valve, with coarse ribs, strong concentric lamella! and stout, long mar- 

 ginal spines. 



Chemung group. Near Bath, Steuben county, N. Y. 



.\trypa marginaus, Dalinaii. 



Kigs. 24, 2&. Dorsal and profile views of a preparation showing the brachidium which has been exposed by 

 the removal of the brachial valve. The spiral cones are more regularly conical an<l more 

 obtuse at their apices than is usual in A. reticularis. In this specimen, also, the lateral 

 branches of the loop are discrete. The figures also show the great elevation of the linguiform 

 extension of the median sinus on the pedicle- valve. X 2^. 

 Middle Silurian. Anticosti. 



Atrypa pseudomarginalis, Hall. 



Figs. 26, 27. Dorsal and profile views of the original specimen ; showing the convexity of the valves and 

 the strong median fold on the brachial valve. 



Comiferous limestone. Schoharie, N. Y. 



