16 Brachiopoda of the Cincinnati Group. 



Trematis millepiinetata. — (Hall, 1866). 



Shell suborbiciilar, transverse on the ventral side and lenticular in 

 profile, and varying in size from one quarter to one half inch or more 

 in diameter. 



Ventral valve strongly convex below the middle, more depressed 

 above ; with a narrow, deeply depressed pedicle opening, the margins 

 of wdiich are flattened for a space nearly equal to the breadth of the 

 opening. 



Dorsal valve more elongate, most convex above the middle ; the 

 l)eak pointed and projecting considerably beyond the opposite valve ; 

 Avith a depressed or concave triangular area. 



Interior of the dorsal valve marked near the middle by two com- 

 paratively large, semicircular or reniform muscular scars, the breadth 

 across the two more than equal to one third of the diameter of the 

 valve ; the center of the valve has also a slight mesial septum. 



Surface strongly punctate in concentric curves passing from the 

 center of the shell outward, extending through the shell near the 

 front of the valves, and distinctly marking the cast ; inner layers of 

 the shell not punctate. 



It differs from the T. terminalis, in being more transverse, with a 

 less convexity of the ventral valve and more prominent beak of the 

 dorsal valve ; and also in the character of the punctate structure. 

 The Trenton species is distinctly punctured, the puncta passing through 

 the shell, showing most distinctly on partially exfoliated specimens ; 

 while in this species they are entirely confined to the exterior layers 

 of the shell. It is also destitute of the radiating striiTe found in T. ter- 

 minalh, when the shell is partially exfoliated. 



The largest specimen known to me is 0.82 inch in length; 0.92 inch 

 in width ; and 28 inch in convexity. 



Family Rhynchonellidce. 



Shell impunctate, oblong, or trigonal, beaked; hinge line curved; 

 no area; valves articulated, convex, often sharply plaited; foramen 

 beneath the beak, usually completed by a deltidium, sometimes con- 

 cealed ; hinge teeth sujjported by dental plates ; hinge plate deeply 

 divided, supporting oral lamellae, rarely provided with spiral processes; 

 muscular impressions grouped as in Terehratula ; vascular impressions, 

 consisting of two principal trunks in each valve, narrow, dichotomising, 

 angular, the principal posterior branches inclosing ovarian spaces. 



