I02 SMITHSONIAN MISCELI^ANEOUS COLLECTIONS VOL. 53 



BILLINGSELLA MARION, new species 



Plate io, Figure S 



Dorsal valve transverse; beak small, marginal; sides broad, 

 rounded, and merging into the broadly round, almost transverse 

 frontal margin ; cardinal line a little shorter than the greatest width 

 of the valve and sloping very slightly from the beak to the outer ex- 

 tremities ; on one specimen the cardinal angle is extended slightly ; 

 greatest width about midway of the length ; mesial furrow narrow 

 at the beak and gradually widening to a broad, deep furrow which 

 divides the valve into two lobes. 



Surface smooth with the exception of a few (six or seven) 

 obscure radiating ribs on each lobe. A specimen lo mm. in width 

 has a length of 6 mm. 



Observations. — This species is represented by three specimens of 

 the dorsal valve. They all indicate a thick shell of the Billingsella 

 salcnicnsis (Walcott) [1887, p. 190] type. I do not know of a 

 similar form in the Cordilleran Cambrian fauna. It is associated 

 with Microniitra (Pateriiia) stissingensis (Dwight) [1889, p. 145], 

 a species of Microdiscus, and Ptychoparia, in a compact gray lime- 

 stone. 



Formation and Locality. — Middle Cambrian: About 1,750 feet 

 (533.4 m.) above the top of the Lower Cambrian, in the oolitic lime- 

 stones of the Stephen formation [Walcott, 1908a, p. 3], below the 

 horizon of the Ogygopsis fauna, east side of Mount Stephen, about 

 3,000 feet (914.4 m.) above the Canadian Pacific Railway track and 

 3.5 miles (5.63 km.) east of Field, British Columbia, Canada. 



EOORTHIS, new genus 



Not Plcctorthis Hall and Ci,arkE, 1892, Nat. Hist. New York, Paleon- 

 tology, VIII, Pt. I, pp. 194-195. (Characterized as a new genus; see 

 below for copy. This genus, as now restricted, is not known to occur 

 in the Cambrian.) 



Orthis (Plectorthis) Walcott [not (Hall and Clarke)], 1905, Proc. V. S. 

 National Museum, XXVIII, pp. 257-259. (Original characterization 

 copied and genus discussed somewhat as below.) 



Plcctorthis Grabau and Shimer (in part) [not (Hall and Clarke)], 1907, 

 North American Index Fossils, II, Bryozoa and Brachiopoda, pp. 250 

 and 251. (Characterized.) 



In their subdivision of the genus Orthis Dalman, Messrs. Hall and 

 Clarke [1892&, p. 192] restricted the genus Orthis to the group of 

 which Orthis caUactis Dalinan is the type, and, among American 

 forms, Orthis tricenaria of the Trenton and Hudson faunas. These 



