The Fauna of the Maxville Limestone. 391 



A few broken internal molds have been referred to this 

 species. 



Horizon and locality. — Maxville limestone. 

 Upper zone: Below Thompson Residence (?), White Cottage. 



PINNA MAXVILLENSiS— Whitfield. 



1882. Pinna MaxviUensis. Whitfield, Ann. N. Y. Acad. Sci., Vol. II, 

 p. 221. 



Maxville limestone : Maxville, Ohio. 



1891. Pinna MaxviUensis. Whitfield, Ann. N. Y. Acad. Sci., Vol. V, 



p. 586, pi. 14, fig. 5. 



Maxville limestone : Maxville, Ohio. 



1895. Pinna MaxviUensis. Whitfield, Geol. Surv. Ohio, Vol. VII, p. 474, 

 pi. 10, fig. 5. 



Maxville limestone : Maxville, Ohio. 



Description. — "Shell of about medium size, very acutely tri- 

 angular in outline, with highly convex valves ; the length along 

 the hinge equal to nearly three times the greatest width. Hinge 

 line straight, not quite as long as the shell below ; anterior end 

 acute; basal margin very slightly arcuate, and the posterior 

 extremity rather broadly rounded; the point of greatest length 



Fig. 17. — Pinna maxvillensis. A view of a left valve. (After Whitfield.) 



being at about one-third of the width below the hinge-line. 

 Surface of shell, except for a short distance within the basal 

 margin, marked by moderately strong, simple radiating plica- 

 tions, about eighteen in number, as counted at the posterior end 

 of the specimen figured, but increasing in number with icreased 

 growth ; the additions being near the hinge. There are also 

 numerous strong concentric lines of growth parallel to the mar- 



