296 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 33 



spines and more arched pleural spines of H. rozvei and the outlines 

 of the pygidia. 



Formation and Locality. — Lower Cambrian: (if) arenaceous 

 shales of the Silver Peak Group, forming No. 12 of the Barrel 

 Spring section [Walcott, 1908c, p. 189], 3 miles (4.8 km.) north- 

 west of Barrel Spring, which is 10 miles (16 km.) south of the 

 town of Silver Peak, Esmeralda County, Nevada. 



WANNERIA, new genus 



Dorsal shield large, broadly oval in outline. Cephalon about two- 

 fifths of the length of the dorsal shield, transversely semicircular 

 in outline with genal angles extended into strong spines ; marginal 

 border strong ; cheeks broad ; glabella elongate, semicylindrical and 

 with four lobes, the anterior being the largest and expanded slightly 

 or not at all beyond the line of the sides of the glabella ; palpebral 

 lobe connected to the anterior lobe of the glabella ; it is short and 

 relatively small in the adult [pi. 30, fig. 2; pi. 31, fig. 3] and in- 

 creasing in length with the decrease in the size of the cephalon [pi. 

 30, figs. 3, 4; pi. 31, figs. 3, I, 2. 4, 7, 8; pi. 38, figs. 19, 22]. 



Thorax with seventeen segments ; median lobe strongly convex ; 

 pleural lobe broad and with the pleurae extended into falcate ends 

 that curve more and more backward until the posterior pairs nearly 

 enclose the pygidium ; pleural furrow broad, next to the axial lobe, 

 and extending out about one-half the length of the pleura. 



A small median, elongate tubercle occurs on the axial lobe of each 

 segment, that becomes a strong, long, median spine on the fifteenth 

 segment in old, large specimens [fig. 11, pi. 30]. It is small in 

 younger individuals [fig. 10, pi. 30]. 



Pygidium small, subcircular, transverse where it joins the thorax 

 and notched at the posterior center. 



Surface with irregular network of very fine, irregular ridges that 

 form very fine meshes over the greater part of the outer surface of 

 the dorsal shield and hypostoma ; the meshes are elongated on the 

 marginal border of the cephalon and genal spines subparallel to the 

 margin, while on the doublure of the thoracic pleurae the meshes are 

 more or less transverse [pi. 31, fig. 12], also on the pygidium [pi. 

 30, fig. 8]. 



Dimensions. — Two of the species of the genus, W. walcottanus and 

 IV. halli, grow to a large size, equal to that of any species of the 

 Mesonacidse. The former species is known to have reached a length 

 of 17.6 cm. with a width of 15 cm. at the genal angles. Fragments 

 of W. halli indicate a length for the dorsal shield of 15 cm. 



