FOSSILS OF THE SILURIAN AND DEVONIAN ROCKS. 47 



Dorsal valve moderately concave, sometimes nearly flat, often with a slight 

 mesial depression or sinus, which is usually only noticeable in the basal half ; 

 apex small and projecting a little beyond the hinge-line, partly closing the 

 triangular fissure of the other valve. There is a narrow, almost linear area, 

 interrupted in the middle by a wide pseudo-deltidium which covers the ex- 

 tremity of the cardinal process. Surface marked by about eighteen to twenty 

 broad, simple, rounded plications, which are wider than the spaces between 

 them. The central one on the ventral valve is stronger and more elevated than 

 the balance, while on the dorsal valve there is a corresponding wider and 

 deeper groove. Bifurcation is only noticed in rare instances. Fine undulating, 

 concentric striae ornament the surface, and some stronger imbricating lamellae 

 mark the different stages of growth. It appears that our Kentucky specimens 

 differ slightly from the New York ones, which latter have rounded extremities 

 and almost straight lateral margins, while in the Kentucky specimens extremi- 

 ties and lateral margins are as before mentioned. 



Formation and Locality. In the upper strata of the Devonian limestone in Clark county, In- 

 diana, and some few places south-east of the city of Louisville, Ky. The Indiana specimens are very 

 tine and perfect, often showing the two valves separated, except -at the hinge. Our shells are almost all 

 silicified and have different sizes ; the one represented on plate XVII. belongs to the larger ones. 



Genus Anastrophia. Han. 



Anastrophia, Hall. Pal. N. Y., Yol IV., p. 3731867. 



Etymology: ana, witfi; strophe, a turning round, alluding to the valves having reverse relation; the 

 dorsal valve is larger than the other, and its beak overlaps the ventral beak. 



Shell rotund or gibbous, with the valves, as in ordinary Pentamerus, reversed. 

 The ventral valve is the smaller, gibbous in its upper part, depressed or sinuate 

 below, with the Y-shaped pit sessile for nearly its entire length ; a small flat- 

 tened space on each side of the fissure. The dorsal valve is ventricose, larger 

 than the ventral, with prominent umbo. The hinge-plate is extended in gradu- 

 ally converging vertical lamellae, which are joined to the shell throughout their 

 length, while the crura are extended into the cavity in thin free lamellae. The 

 species : Pent, verneuilli, P. internascens and P. reversus are the types of this 



new genus. 



Anastrophia internascens. HALL. 



Plate XXXII., figures 17 to 20. 



Anastrophia internascens, Hall, llth Geol. Kep. of Indiana 1881. 

 See list of synonyms in said llth Rep. of Indiana. 



Shell transversely sub-elliptical, ovoid or sub-globose in different stages of 

 growth ; the length and width are sometimes nearly equal. Valves of young 

 specimens nearly equal in convexity, in older individuals the dorsal valve 



