BRACHIOPODA—PROTREMATA. 243 



XLV1I. Productus Sowerby. 

 Semicircular without functional pedicle but probably anchored 

 by spines of pedicle valve. Pedicle valve large, convex, with 

 inflated and greatly incurved umbo. Brachial valve small, concave 

 or almost flat. Hinge line straight ; cardinal areas and teeth absent 

 or rudimentary. Cardinal process large, four-lobed when viewed 

 from within. A median ridge in each valve separates the muscular 

 areas. Surface with radiating ribs crossed by concentric lines or 

 wrinkles, the surface of pedicle valve often studded with spines. 

 Carbonic, 



A. Large (over two inches wide) *. 



* Surface marked with regular concentric folds from beak to front. 



160. P. punciaius. 



* Surface marked with very coarse striae and a few concentric wrinkles. 



152. P. semireticulatus. 



B. Medium (between one and two inches wide) **. 



** Sinus present I . 



I. Beak greatly incurved 148. P. burlingtonensis. 



1. Beak small, slightly incurved a, 



a. Radiating striae coarse 154. P. costatus. 



a. Radiating striae very fine 155. P. inflatus. 



** Sinus absent 2. 



2. Hinge line somewhat shorter than width of shell below b. 



b. Spines few and scattering 153. P. cora. 



b. Spines very numerous i / . 



1/. Spines in 2 series ; one series of large, the other of small spines. 



159. P. nebraskaensis. 

 i / . Spines in a single series 161. P. symmetricus. 



2. Hinge line much shorter than width of shell below (equalling only about 



half the width) 147. P. Icevicosta. 



C. Small (less than one inch wide) ***. 



*** Hinge line equal to or exceeding the width of the shell below 3. 



3. Sides flattened, giving the shell a four-sided appearance from the hinge- 



margin. No sinus 157. P. mexicoanus. 



3. Not four- sided c. 



c. Hinge line extended. Broad mesial sinus 156. P. longispina. 



c. Hinge line not extended 158. P. muricatus. 



■*** Hinge line less than width of shell below 4. 



4. Surface marked by concentric wrinkles d. 



d. With a marginal fold 150. P. martini cinctus. 



d. Without a marginal fold 149. P. biseriatus. 



4. Surface marked by radiating striae 151. P. fasciculatus. 



147. P. laevicosta White. Lower Carbonic. 



Subtriangular in general outline, rapidly increasing in width from 



the small, narrow beak to near the front where it is broadly 



