so. 1299. CAMBRIAN BRACHIOPODA—WALCOTT. 609 



The area of the ventral valve is about one-fifth the length of the 

 shell. It is divided midway by a narrow, strongly marked pedicle 

 furrow, and midway between the pedicle and lateral margins by a sharp 

 flexure line. The strife of growth cross parallel to its base. The area 

 of the dorsal valve is relativeh^ short, but extends well out onto the car- 

 dinal margins. Although there is a large series of specimens, and 

 many of them with the surface of the shell exfoliated, nothing is 

 known of the vascular markings or muscle scars. 



Ohservatlcyns.—Vshen studying 0. (Z.) hellus in 1900, I came to the 

 conclusion that O. {L.) co7icinmis and 0. (L.) lens from Cape Breton 

 were identical, but with still larger collections obtained by Mr. S. 

 Ward Loper in 1901 from Cape Breton, especially of 0. {L.) lem^ it 

 appears that the outlines of 0. (Z.) hellus are more uniformly sulxjuad- 

 rate in the adult specimen of the dorsal valve than the Cape Breton 

 form. O. (Z.) eonclruius and O. {L.)hellns^ however, are closely related 

 and both occur in the Upper Cambrian beds. 



Fofiinif'nni and locality.. — Upper Cambrian. Arenaceous shale at 

 sevonil loctdities on McNeils Brook; also, ravine one-half mile north 

 of McMullin's, on crossroad to Boisdale railroad station; in ravine 

 east of railroad, just south of Barachois post-office; Upper Leitches 

 Creek, Cape Breton, Nova Scotia. 



OBOLUS (LINGULELLA) ATAVUS Matthew. 



Leptoholas aluvux Matthew, Bull. Nat. Hint. Soc. New Bruiiswit-k, IV, 1899, 



p. 200, pi. II, figs. 1 a-f. 

 Obolus {Linguleplfy) gregvxi ViALCoTT, Proc. U. S. Nat. Mus., XXIII, 1901, p. 692. 



General form elliptical, with the ventral valve subacuminate and 

 the dorsal valve broadly subacuminate in outline. In the shorter 

 form of the valves the sides are almost uniformly rounded from the 

 cardinal slopes to the frontal margin. The convexity of the valves 

 is fairly strong, that of the dorsal valve being broken by a slight 

 longitudinal flattening that extends from the posterior portion to the 

 frontal margin. As shown by the matrix, the outer surface is marked 

 by concentric ridges and fine striie of growth. The interior cast shows 

 concentric lines and traces of rather coarse radiating lines. None of 

 the specimens preserve the shell, ]mt from the strength of the interior 

 sui'face markings it is inferred that the shell was rather thick. 



The longest ventral valve in the collection has a length of 6 mm., 

 width 3i mm. The dorsal valves are slightly shorter. 



The area of the ventral valve is divided at the center by a strong 

 pedicle furrow, and about midway between the pedicle furrow and the 

 outer margin by clearly marked flexure lines that extend from the 

 apex with a slightly outward curvature to the base of the area. Striae 

 of growth cross the area parallel with its base, being much stronger 

 on the area than in the pedicle furrow. The area of the dorsal valve 



Proc. N. M. vol. xxv— 02 39 



