201 



imbricating lamella} of growth ; muscular impression shallow, semi- 

 elliptical ; inner margin of the valves neatly crenulated, in well-pre- 

 served specimens. 



Length, 2J inches ; width, 2 inches. 



This species is closely allied to O^trea acutirostris, D'Orb., but its 

 transverse diameter is greater, and the back less acute. 



Lower Cretaceous, Pine Bluff, Red River County. Collected by 

 Dr. G. G. Shumard. 



O. PLANOVATA, (n. sp.) Shell small, thin, irregularly ovate, nar- 

 row at rostral end, and somewhat rapidly expanding to the front ; 

 length about one fourth greater than the width ; inferior valve flat- 

 tened beneath, lateral edges of rostral half turned upwards; pallial 

 margin broadly rounded and reduced to a sharp edge, right side 

 straight or very slightly convex; left side broadly arcuate; beak 

 truncated or obtusely rounded, curved to the right ; point of attach- 

 ment to foreign substances indicated beneath by an irregular exca- 

 vation ; cavity of valve somewhat deeply excavated with the raised 

 margin finely crenulated; muscular impression approaching semi- 

 elliptical, and very slightly impressed ; hinge area small, broad, trian- 

 gular and with a narrow, distinctly impressed deltoid excavation, 

 which equals in width the raised space on either side ; surface marked 

 with thin concentric lamella? of growth; superior valve unknown. 



Width from back to pallial margin, 1.36 ; from side to side, 0.92. 



Navarro County, near Dresden, in light gray shale, supposed to be 

 of the age of the Austin Limestone. 



C. LiXEATA, (n. sp.) Shell somewhat trapeziform, gibbous, length 

 about one fourth greater than the width, valves thick ; buccal end 

 short and narrowly rounded ; posterior margin obliquely subtruncate 

 and subangulated at inferior extremity ; posterior cardinal margin 

 very slightly arched, forming, with the anal margin, an obtuse angle ; 

 pallial margin gently rounded; umbonial region very gibbous; a 

 sharp carination extending from the posterior side of the beak to the 

 postero-inferior angle, and limiting an obtusely triangular space be- 

 hind, which is excavated above and plane below ; beaks prominent, 

 elevated, strongly incurved, situated between the middle and anterior 

 margin; surface marked with from ten to twelve sharp concentric 

 lines, separated by spaces which gradually widen from beak to pallial 

 niargin. The spaces are also marked with fine, transverse lines of 

 growth. 



Length, 1.57 inch; width, 1.20; thickness, 1.00. 



This fine species occurs very abundantly in Septaria? of the Cre- 

 taceous Period. Ripley Group, in the bed of a small branch, near 

 Corsicana, Navarro County. 



