BRACHIOPODA—NEOTREMATA. 205 



prominent. Surfaces of both valves marked by concentric lines 

 and fine lamellations. 



Ohio, Indiana, Iowa, Illinois, Missouri. 



XX. Djscinisca Dall. 

 Lower or pedicle valve flattened or concave with an elevated inte- 

 rior pedicle disc perforated by an oval pedicle opening which 

 passes directly through the shell ; externally this pedicle disc 

 shows as a depressed area. Upper or brachial valve convex. 

 Apices of both valves nearly posterior. Shell structure more or 

 less horny. Miocenic and Pliocenic. 



52. D. lugubris Conrad. (Fig. 256 ,f-g.) Miocenic and Pliocenic. 

 Small (about y 2 inch in diameter), subcircular. Brachial valve 



with rather elevated apex which is obtusely pointed and situated 

 at about one fourth the shell's diameter from the posterior margin. 

 Surface strongly lamellose especially over the outer half. Very 

 faint radiating lines are visible. 



New Jersey, Maryland, Virginia, South Carolina. 



XXI. Schizotreta Kutorga. 

 Similar to Orbiculoidea but with thicker shell and with the rela- 

 tive convexity of the valves reversed, i. e., the pedicle valve very 

 convex and the brachial flattened. Ordovicic-Siluric. 



53. S. pelopea Billings. (Fig. 241, a-b.) Ordovicic. 

 Nearly circular with strongly elevated pedicle valve and de- 

 pressed convex brachial valve. Surface marked by numerous 

 strongly elevated concentric lines of growth. Pedicle opening 

 small, oval. 



Trenton and Lorraine of Iowa, Wisconsin, Minnesota, Ontario, 

 Quebec. 



54. S. tenuilamellata (Hall). Siluric. 

 Shell thin, larger and more circular than preceding, with thin, 



elevated, prominent, concentric lamellose growth lines ; pedicle 

 valve elevated with concave foraminal slope, and elongate exter- 

 nal pedicle opening. 



Niagaran beds of New York, Ontario, and Nova Scotia. 



XXII. Rcemerella Hall and Clarke. 

 Similar to Orbiculoidea but with pedicle valve very concave and 

 brachial very convex. Devonic. 



