CAMBRIAN BRA CHIOPODA— WA LCOTT. 245 



BILLINGSELLA SALEMENSIS Walcott. 



OrfJiis saletnen^ifi Wau'oit, Aiiier. Jour. Sci., 3d ser., XXXIV, 1887, p. 190, 

 pi. I, figs. 17, 17a; Tenth Ann. Eept. U. S. Geol. Sur., p. 612, pi. lxxii; figs^. 

 6, 6a. 



Shell about the average size of the Cambrian specii's of the genus. 

 Transversely subquadrilateral; front broadly rounded and slightly 

 sinuate midway; hinge line as long as the greatest width of the shell. 



Ventral valve convex, most elevated about one-fourth the distance 

 from the beak to the anterior margin; beak small and incurved to the 

 margin of the medium-sized area; the surface of the area and the 

 foramen have not been observed; mesial sinus broad and shallow, 

 marked b}^ a low median rib and laterally by two costfe on each side, 

 a third appearing just outside the sinus. 



The dorsal valve, associated in the same hand specimen of limestone, 

 is slightly more convex; frontal margin with a rather deep sinuosity 

 to receive the projection of the ventral valve; median fold broad and 

 l)ut slightly elevated, marked by two or three low costse; the beak 

 appears in the broken specimen in the collection to be scarcelv elevated 

 above the surface of the shell, and to terminate at the cardinal margin; 

 area unknown. 



The surface of both valves is marked by fine concentric lines of 

 growth, and low, rounded costee, varying in number from six to seven. 



In the broad costaj and the general aspect of the shell this species is 

 unlike any known to me from the Cambrian, with the exception of 

 B. inhitfieldi^ from which, however, it differs in strength and character 

 of costse and outline of valves. 



Formation and localities. — Lower Cambrian; limestone interbedded 

 in the shal}^ slates li miles south of Salem; 1 mile south of Shushan, 

 and near Rock Hill school house (No. 8), Greenwich, Washington 

 County; bedded limestone of Olenellus zone on north side of Beman 

 Park, Troy, New York. It is also present in limestone bowlders of the 

 Cambrian conglomerate at Metis, on the St. Lawrence, below Quebec. 

 Olenellus sp. HyolitheUus inicans., etc., occur in association with it. 



Cat. U. S. Nat. Mus., No. 17443. 



BILLINGSELLA STRIATA, new species. 



The form of the ventral valve of this species is much like that of 

 B. jdicatella. It differs in having a finely striated outer surface, and 

 in the strong development of the main vascular sinuses and the broader 

 (leltidial cavity. The only two specimens of the dorsal valve are 

 iiearl}^ flat. 



Formation and locality. — Middle Cambrian? The character of the 

 matrix indicates that the specimen came from the Flathead formation. 

 Forks of Pole Creek above Cherry Creek Valley, Madison County, 

 Montana. 



