PLATE hV— Continued. 



AxKYPA ASrERA, Schlot liciiu, var. occidentalis, Hall. 



Figs. J8, Ifl. Dnraal ami profile views of a Devonian shell ; showing' the gibbosity of the liracliial valve, the 



coarse plications ami strong concentric lamellie. 

 Fig. 20. A preparation of the brachidinm expose<l by the removal of the pe(ii<'.le-valve ; showing the form 



of the cones and loop. (Whitfield ) 



Upper Devonian. Independence, Iowa. 



Atrypa spino.sa, Hall. 



Fig. 21. The exterior of the pedicle-valve; showing the extension of the concentric lamellfe into well- 

 defined spinules. When these .'^pinnies ai'e removed such shells present coarse, strong plications 

 like those of A. aspera. 



Hamilton group. Moscino, N. Y. 

 Fig. 22. Dorsal view of a specimen with longer spines. A portion of the biachial valve has been removed, 

 showing one of the spiral cones, which is con.<;iderably depressed. 

 Hamilton group. Cmmndaigua Lake, N. Y. 



Atrypa hystrix, Hall. 



Fig. 23. The exterior of a pedicle-valve, with coarse ribs, strong concentric lamellfe and stout, long mar- 

 ginal spines. 



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



Atrypa marginalis, Dalman. 



Figs. 24, 25. Dorsal and profile views of a preparation showing the brachidium which has been exposed by 

 the i-emoval of the brachial valve. The spiral cones are more regularly conical and more 

 obtuse at their apices than is usual in A. rtticularU. In this specimen, also, the latei'al 

 branches of the loop are disci'ete. 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 PSEUDf)MARGiNALis, Hall. 



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

 the strong median fold on the brachial valve. 



Corniferous limestone. Schoharie, N. Y. 



