NO. 1395. CAMBRIAN BRACHIOPODA—WALCOTT. 287 



LOPERIA, new subgenus of PROTORTHIS. 



This subg'enus is characterized by the form of the valves. The ven- 

 tral valve is elevated at the umbo and flat or slightly concave from the 

 umbo to the margins; the dorsal valve is strongly and regularly convex. 

 The description of the type species, ProtortJds {Loperia) dougaldensia^ 

 is that of the subgenus and species, as it is the only species thus far 

 known of the subgenus. 



PROTORTHIS (LOPERIA) DOUGALDENSIS, new species. 



General form rounded subquadrate. Hinge line straight and 

 shorter than the greatest width of the shell; cardinal extremities 

 obtusel}" angular. Relati\e convexity of the valves reversed, as in 

 Dinoi'thiH pectinella of the Ordovician fauna. Surface of the dorsal 

 valves with strong, simple, rounded ribs that increase by interpola- 

 tion; fine concentric stria^ and lines of growth that sometimes form 

 ridges, cross the ribs, curving in the interspaces and over the ribs; 

 these ribs are more prominent and numerous (30 to 40) on the dorsal 

 than on the ventral valve; on the latter the ribs are broad, with nar- 

 row interspaces, and about 20 to 25 in number; casts of the exterior 

 and interior surfaces have numerous fine, thickly set, elevated papilla? 

 that appear as the casts of the punctte in the layers of the shell; on 

 some specimens the papillw are cylindrical and elevated, which indi- 

 cates that they penetrated deep into the shell substance. All indica- 

 tions point to a punctate, shell; in all the material representing the 

 species the shell has been removed ])y solution, only the casts of the 

 inner and outer surfaces remaining. 



The largest xentral valve in the collection has a length of IS nun., 

 width 25 mm.; dorsal valve, length 22 nun., width 27 mm. 



Ventral valve elevated at the umbo and gently concave from the 

 umbo to the front margin and flat to the cardinal extremities. Area 

 relatively low and overhanging the hinge line at an angle of about 45"; 

 it is divided midway by a broad delthyrium that is more or less closed 

 by a deeply concave plate, across which the transverse stria? of growth 

 of the area pass. The concave plate appears to be identical in form 

 and position with the free spondylium of t^he genus Protorthls. A cast 

 of the interior shows very strong teeth and supporting dental plates; 

 the edges of the dental plates appear to lie continuous with the concave 

 plate or free spondylium. 



Dorsal valve strongly and regularly convex, with a slight flattening 

 of the median line and sometimes a shallow sinus. Casts of the 

 interior show a strong area with a triangular delth3a'ium; the umbonal 

 cavit)' is strongly /)utlined by the crural plates so as to form a pseu- 

 docruralium; crura well developed, with clearly defined teeth sockets 

 back of them. No traces of a cardinal process have been seen in ten 



