NO. 1395. CA MBRI. 1 .Y BRA CHTOPOBA— WA LCO TT. 821 



The muscle scars now known are the transniedian and central; the 

 former are situated close to the marg-in of the valve, and the s})ace 

 assig-iied them may also include the posterior laterals; the central scars 

 are well indicated in several specimens, but no trace has been found of 

 the antero-laterals. The cardinal tubercle includes the spuce that was 

 occupied b_y the several points of attachment of the posterior muscles, 

 i. e., transmedian, outside, and middle laterals; the east of the tubercle 

 is an elong-ate depression just inside the maroin of the shell. 



Ohservatloiix. — By incorrect interpretation both Mr. Billings and 

 myself identified the dorsal valve of the species as the ventral, and I 

 followed him in illustrating a dorsal valve of Oholellacrami as the dor- 

 sal valve of (J. Circe. When studying some material representing the 

 species in the collections of the United States National Museum I 

 noticed the edge of a shell that, on working it free from the matrix, 

 proved to be a ventral valve; two dorsal valves occur on the same ])it 

 of rock. Subsequently Dr. .1. F. Whiteavessent me a tablet from the 

 collections of tlio (xeolog-ical Surve}^ of Canada, on which six specimens 

 were labeled OholeUa dree. No, 1 is a cast of the interior of the dor- 

 sal valve of OholeUa crasi^a^ and No. 2 the exterior of same. Nos. 3 and 

 6 are ventral valves of Qiieheda circe, and Nos. 4 and 5 dorsal valves. 



With the ventral valve identitied, it appears that the shell is not an 

 OholeUa but is the type of an undescribed genus, in which the ventral 

 valve is elevated at the apex, and with strong cardinal tubercles for the 

 attachment of the posterior nmscle scars, very nmch as in Acrotreta. 

 This feature, and the presence of what appears to be the base of the 

 cast of a foraminal tube, suggest that the ventral valve was perforate. 

 Quehecia appears to be on the line of evolution from Oholdla to the 

 calcareous, perforate, inarticulate shells represented by Yorh'ia. 

 OholeUa, Qiieheda, and Yorl'/a are all strong, calcareous, perforate 

 shells of the older Cambrian fauna, and are evidently closely related. 



Formation aiiel locality. — Lower Cambrian. Limestone bowlders in 

 conglomerate at Trois Pistoles, on the St. Lawrence River, below 

 Quebec, Canada. 



Genus ELKANIA Ford. 



BUlimjsia Ford (not de Koninck, 1876), Aiiier. Jour. Sci., 8d ser., XXXI, 1886, 



p. 466. 

 Elkania Ford, Amer. Jour. Sci., 3d ser., XXXII, 1886, p. 325. 

 Elkania Hall and Clarke, Pal. New York, VIII, 1892, Pt. 1, pp. 75, 165; 



Eleventh Ann. Rep. New York State Geologist, 1894, p. 241. 



General form ovate, biconvex; shell substance corneous and made 

 up of several thin layers or lamelhe that increase in number toward 

 the front and lateral margins. Surface marked by line concentric 

 stria? of growth. Apex of both ventral and dorsal valves marginal. 

 The interior of the ventral valve has a thickened posterior section which 

 has a central pedicle furrow, and two tiexure lines running obliquely 



