428 CAMBEIAN BRACHIOPODA. 



Matthew [1892, p. 94] uses the name Oholus lens-primus for a small shell of this species 

 which was found in a lower layer of rock. The form is not illustrated or described in his larger 

 work [Matthew, 1903], and I could not discover from the specimen that it was anything more 

 than a young shell of the variety lens. 



Formation and locality.— Middle Cambrian: (13e) Sandstones of Division E2c; (131 and 344i [Matthew, 1903, 

 p. 80]) sandy shales of Division E3a; (344 [Matthew, 1903, p. 144]) sandy shales of Division E3b; and (ISn')" sand- 

 stones of Division E3e: all in Matthew's [1903, p. 21] Etcheminian, on Dugald Brook, Indian River, eastern Cape 

 Breton, Nova Scotia. 



(13m) Sandstones of Division ESf of Matthew's [1903, p. 76] Etcheminian, on Gillis Brook, Indian River, eastern 

 Cape Breton, Nova Scotia. 



FOBDINIA Walcott, subgenus of OBOIiTJS. 



Elkania Ford, Walcott (in part), 1905, Proc. U. S. Nat. Mus., vol. 28, pp. 321-323. (Described and discussed; see 

 under Elkania, p. 561, for copy. The text includes reference to species now placed under both Elkania and 

 Obolus (Fordinia).) 



Obolus (Fordinia) Walcott, 1908, Smithsonian Misc. Coll., vol. 53, No. 3, pp. 64-65. (Characterized and discussed 

 as below as a new subgenus.) 



Obolus (Fordinia) Walcott, 1908, idem. No. 4, PI. XI, and pp. 142 and 144. (Classification of subgenus.) 



This subgenus of Oholus is proposed for species having a Lingulella-like outline and form 

 with the development of a tendency to form a platform or thickening in the valves in connec- 

 tion Avith tlie attachment of the muscles in the ventral valve and a thickening in tlie posterior 

 portion of the dorsal valve back of the central muscle scars. The type of the subgenus, 0. (F.) 

 perfectus Walcott (PI. LXIII, figs. 10, lOa-d), has these characters well developed. The second 

 species, 0. (F.) hellulus (Walcott) (PL LI, figs. 3, 3a-f), has the cardinal area of the ventral 

 valve more united with the visceral area than it is in 0. (F.) perfectus, and the raised area in 

 the dorsal valve is much smaller. In 0. (F.) gilberti Walcott the thickened areas are much 

 smaller than in the other two species. These three species represent a form intermediate' 

 between Oholus (Pis. VII and VIII) and Elkania (PI. LI). 



Type. — Oholus {Fordinia) perfectus Walcott. 



The subgeneric name was given in honor of Mr. S. W. Ford. 



Obolus (Fordinia) bellulus (Walcott). 

 Plate LI, figures 3, 3a-f. 



Elkania bellula Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, p. 323. (Described and discussed as below as a new- 

 species.) 



General form elongate oval, biconvex; beaks marginal. Surface marked by fine concen- 

 tric strife of growth that occasionally form varices and small ridges near the umbo ; the inner 

 layers or lamellae have radiating strife in addition to concentric stri^. 



The shell is relatively thin and small. It rarely exceeds 2.5 mm. in length and a little less 

 in width ; the dorsal valve is somewhat shorter than the ventral. 



Ventral valve subacuminate, moderately convex; the interior shows a reversed cardinal 

 area attached to the bottom of the valve and below the plane of the margins of the valve; the 

 pedicle groove is strong; the line of demarcation between the cardinal area and the bottom of 

 the valve is indefinite, as the margin of the area and the body of the shell have been merged 

 into each other ; the transmedian and anterolateral muscle scars are outside the main vascular 

 sinuses and near the margin of the valve; the central scars and middle and outside lateral scara 

 are supposed to have been attached within the area (x) (PL LI, figs. 3a, 3b), as in Oholus; the 

 area is largely on the front slope of the thickening of the umbonal portion of the valve. 



Tlie dorsal valve has a sliort reversed area, as sliown in Plate LI, figure Be; the antero- 

 lateral muscle scars were probably weU advanced toward the front, judging from traces of the 

 length of the visceral cavity. 



a I3n' is the type locality, though the specimens in the United States National Museum to which that number is assigned were collected; 

 somewhat later than Doctor Matthew's. 



