BRACHIOPODA—PROTREMATA. 



21 I 



6j. N. festinata Billings. (Fig. 249.) Lower Cambric. 



Hinge line straight, usually equalling the greatest width of the 

 shell. Pedicle valve elevated at the umbo with a high cardinal 

 area. Surface covered with narrow radiating ribs, increasing both 

 by bifurcation and intercalation. The spines are located on the 

 ribs more or less irregu- 

 larly. An average shell 

 measures about one inch 

 in width with length about 

 one third less. 



New York, Pennsylva- 

 nia, Vermont, Quebec. 



XXX. 



Protorthis Hall 

 and Clarke. 

 Like Billingsella but dif- 

 fering in the absence of a 

 true cardinal process and 

 in the punctate character of the shell substance 

 Cambric. 



Fig. 250. 

 of form. 



Protorthis billihgsi, showing variation 

 (Dawson and Walcott. ) 



Middle-Upper 



68. P. (Billingsella) billingsi (Hartt). (Fig. 250.) 



Middle Cambric. 



Broader than long, with greatest width at hinge line. Most con- 

 vex at about the middle and depressed in front. Brachial valve 

 with sinus. Cardinal area very narrow. Surface marked by about 

 thirty radiating striae crossed by distinct lines of growth. 



New Brunswick. 



XXXI. Rafinesquina Hall and Clarke. 



Semi-oval ; hinge line straight ; cardinal area well developed 

 on each valve. Pedicle valve convex ; brachial concave. Mus- 

 cular area of pedicle valve faintly delimited, consisting of two 

 broad, flabellate diductor scars enclosing an elongate adductor; 

 from the margin of the muscular area radiate irregular furrows and 

 nodose ridges. Brachial valve with bilobed cardinal process. 

 Entire surface covered with striae alternating in size and crossed by 

 finer concentric growth lines. Ordovicic-Siluric. 



69. R. alternata (Emmons). (Fig. 251.) Ordovicic. 



Broadly semi-oval. Pedicle valve convex, flattened near the 



