72 



Descriptions of New Species of Fossils 



occuping one-third of the area. Dorsal valve moderately convex, 

 the greatest convexity just above the middle ; mesial fold indistinct 

 above, becoming prominent towards the base, marked on each side 

 by 'one or two obscure undulations. Surface marked by concentric 

 undulating ridges, and intermediate fine radiating strife. 



This form resembles JSp. hicostata' of the Niagara Limestone of 

 New York, but is much smaller and with the ventral valve more ele- 

 vated. 



Teiplesia putilltjs n. sp). 



CompsiTe Spii'if era ? Waldronensis 'Mii.ij'E.Ti and Dyer. Contributions to Palseon- 

 tology, Journal of the Cincinnati Society of Natural History, April, 1878. 



Shell small, subquadrate in outline, length and breadth nearly 

 equal, hinge-line straight, less than the width of the shell, extremi- 

 ties rounded. Ventral valve slightly convex on each side of the 

 sinus, becoming concave near the margins ; mesial sinus undefined 

 above, becoming wide and deep below, and produced in front into a 

 long triangular extension ; beak greatly elevated, acute, extending 

 beyond the hinge-line, the apex obscurely marked by what appears 

 to be a minute foramen ; area triangular, wider than high, deltidium 

 triangular, higher than wide. Dorsal valve very gibbous ; moder- 

 ately convex on each side of the fold, and slightly concave just with- 

 in the margins; mesial fold commencing about one-third the length 

 of the valve below the beak and becoming very prominent towards 

 the base ; summit of the fold straight, its greatest elevation being 

 at the basal margin ; beak obtuse, closely incurved. 



Surface marked by fine concentric lines of growth, which toward 

 the margins become strong lamellose strife. 



The specimens of this species are distorted in their mode of growth, 

 apparently from the natural obliquity of the mesial fold and sinus. 



Pextameeus foexicatus var. 

 Pentamerus fornicatus Hall. Pal. N. T., vol. ii, page 81, plate 24, fig. 7. 



Shell ventricose, larger valve highly arcuate, length less than the 

 width, umbo gibbous, beak strongly incurved ; a broad shallow and 

 undefined mesial sinus extends from the umbo to the base of the 

 shell, having in the centre a low, distinct elevation which gives a 

 double sinus : the median elevation is scarcely so high as the shell 

 on each side, prolonged in front, and terminating in a distinct emar- 



