PLATE LV—Continued. 
AteyPxV aspera, Schlotheiiii, vur. occidentalis, Hall. 
o 
Figs. 18, 19. Dorsal and profile views of a Devonian shell; showing the gibbosity of the brachial valve, the 
coarse plications and strong concentric lamellae. 
Fig. 20. A preparation of the brachidium exposed by the removal of the pedicle-valve ; showing the foj’m 
of the cones and loop. (Whitfield.) 
Upper Devonian. Indejpmdence, Iowa. 
Atrypa spinosa, Hull. 
I'''ig. 21. The exterior of the pedicle-valve ; showing the extension of the concentric lamellae into well- 
defined spinules. When these spinules are removed such shells present coarse, strong plications 
like those of A. aspera. 
Hamilton group. Moscow, iV. U. 
Fig. 22. Dorsal view of a specimen with longer spines. A portion of the brachial valve has been removed, 
showing one of the spiral cones, which is considerably depressed. 
Hamilton group. Ca7ia7idaigua Lake, N. Y. 
Atrypa hystrix, Hall. 
Fig. 23. The exterior of a pedicle-valve, with coarse ribs, strong concentric lamellae and stout, long mar¬ 
ginal spines. 
Chemung group. Near Bath, Steube^i county, N. Y. 
Atrypa 
Dal man. 
marginalis, 
Figs. 24, 25. 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 and more 
obtuse at their apices than is usual in A. I'eticulai'is. In this specimen, also, the lateral 
bi'anches of the loop are discrete. The fig'ui es 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. 
Corniferous limestone. Schoharie, N. Y. 
