98 PALEONTOLOGY OP KENTUCKY. 



Meristella nasuta. CNKAD. 



Plate XV., figures 2 to 8. 



Atrypa nasuta., Conrad. Ann. Kep. on Pal. N". Y., p. 18. 

 Meristella nasuta, Hall. Thirteenth Rep. on St. Cab., p. 93 186t. 

 Meristella elissa, Hall. Fourteenth Rep. on St. Cab., p. 1001861. 

 Meristella nasuta, Hall. Fifteenth Rep. on St. Cab., p. 160 1862. 

 Athyris clara, Billings. Canadian Journ., p. 274 1860. 

 Athyris clara, Geology of Canada, p. 373 1863. 

 Meristella nasuta, Hall. Pal. N. Y., Vol. IV., p. 2991867. 



Shell large, sub-oval, ovate or sub-rhomboidal ; the greatest width near or a 

 little below the middle ; length equalling or slightly exceeding width. Both 

 valves convex, the ventral one rather gibbous. A nasute or linguiform exten- 

 sion of tiie front in old shells. 



Ventral valve exceeding the other one considerably in convexity ; point of 

 greatest curvature being a little above the middle, from where it slopes in 

 strong curves towards the lateral margins and to the cardinal lines, but in 

 somewhat gentler curves to the front. 



Umbo extremely prominent; beak regularly rounded and closely incurved. 

 The anterior portion of the valve is produced into a nasute or linguiform ex- 

 tension ; no depression for a mesial sinus is noticeable. In young or half grown 

 individuals no basal extension exists. Dorsal valve less convex than the oppo- 

 site, moderately and regularly convex in young shell, becoming in old shells 

 gibbous above, curving regularly to the sides, and often a little flattened at the 

 baso-lateral margins ; at about the middle of the length, or sometimes above, 

 the central portion of the valve becomes more gibbous, and towards the front 

 is abruptly elevated into a rounded prominent fold, corresponding to the lin- 

 guiform extension of the opposite valve. The beak is moderately incurved, 

 lying close beneath that of the opposite valve. 



The general aspect of the surface is that of a smooth shell with a few concen- 

 tric lines of growth ; in perfect individuals, however, the entire surface is 

 ornamented by very fine concentric lines, and usually by indistinct radiating 

 striae, which are often more conspicuous in the partially exfoliated shell, and 

 still more distinct in some of the casts. The interior of the ventral valve pre- 

 serves the generic characters in a marked degree, in the open fissure beneath 

 the beak, which is terminated by a sub-circular perforation ; in the strong 

 dental plates, and deeply marked muscular impression. The inner surface, 

 surrounding the muscular impression is covered by radiating striae. The 

 interior of the dorsal valve shows a strong cardinal process, with a shallow, 

 spoon-shaped depression in center, margined by deep teeth sockets. The mus- 

 cular area is elongate-ovate, broader above, and divided through the center by 

 a thin elevated septum. 



