OBOLID.^. 561 



Mr. Delgado very kindly sent me a specimen of this species, also some large photographs 

 of specimens illustrated by him. I have reproduced three of these in illustration of the species. 



Formation and locauty. — Lower Cambrian: (351 [Delgado, 1904, p. 365]) Shales at Monte de Valbom, north- 

 east of Villa Boim, Province of Alemtejo, Portugal. 



SubfamUy ELKANIIN^ Walcott and Scliucliert. 



Genus ELKANIA Ford." 



Billingsia Fokd [not De Koninck, 1876], 1886, Am. Join-. Sci., 3d ser,, vol. 31, pp. 466^67. (Described and discussed ■ 



as a new genus.) 

 Not Billingsia Walcott, 1886, Bull. U. S. Geol. Survey No. 30, pp. 5, 21, 60, and 62. (Used in lists for a genus of the 



Gastropoda.) • 



Elkania Ford, 1886, Am. Jour. Sci., 3d ser., vol. 32, p. 325. (Proposes Elhania for Billingsia, which was preoccupied.) 

 Elhania Ford, Hall and Clarke, 1892, Eleventh Ann. Rept. State Geologist New York for 1891, p. 241. (Described.) 

 Elkania Ford, Hall and Clarke, 1892, Forty-fifth Ann. Rept. New York State Museum tor 1891, p. 557. (Copy of 



preceding reference.) 

 Elkania Ford, Hall and Clarke, 1892, Nat. Hist. New York, Paleontology, vol. 8, pt. 1, pp. 75-78. (Copies part of 



Billings's, 1861b, p. 70, description of "Obolella desiderata" and Ford's, 1886a, p. 467, description of the genus, 



and describes and discusses genus.) 

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

 tially as below. The text includes reference to species now placed under Obolus {Fordinia).) 

 Elhania Ford, Walcott, 1908, Smithsonian Misc. Coll., vol. 53, No. 4, PL XI, and pp. 142 and 144. (Classification of 



genus.) 



General form ovate, biconvex; shell substance corneous and made up of several thin layers 

 or lameUse that increase in number toward the front and lateral margins. Surface marked by 

 fine concentric striae of growth. Apex of both ventral and dorsal valves marginal. The inte- 

 rior of the ventral valve has a thickened posterior section which has a central pedicle furrow 

 and two flexure lines running obliquely forward and outward from the apex, a little inside of 

 the grooves of the main vascular trunks; this structure is apparently the result of the union of 

 the area with the bottom of the shell so as to bring, as the shell grew, the path of advance of the 

 pedicle groove, main vascular sinuses, and lateral muscle scars all on one surface instead of on 

 the area and the shell beneath it as in Obolus. 



The muscle scars are arranged as in Oholus. The transmedian and anterior laterals occur 

 well out toward the margin (PI. LI, fig. 1) and the space inclosing the central, middle lateral, 

 and outside lateral scars is in the central area, on the front of the slope of the thickened posterior 

 portion of the valve (PI. LI, figs. 1 and 3a) ; the points of attachment of the individual muscles 

 can not be distinguished. In the dorsal valve the central and anteri9r lateral scars are clearly 

 shown in several specimens; the transmedian and outside laterals are situated just outside 

 the main vascular sinus (PI. LI, fig. Ic). Our knowledge of the vascular markings is limited to 

 the main vascular sinuses, except in one ventral valve, where the inner branches have been 

 preserved; in both valves the main trunk rises near the apex and its path is outlined across the 

 internal cardinal area. 



The preceding description differs materially from that of Ford [1886a, p. 467] and Hall and 

 Clarke [1892c, p. 77]. I find the muscle scars as described above and am compelled to consider 

 them as indicating the same muscles as in Obolus. That the genus is an advance on Obolus in the 

 evolution of the inarticulate brachiopods I quite agree with Hall and Clarke [1892c, p. 165], but 

 not that it is a stage in the transition from Obolus to Trimerella and its allies. (See remarks 

 on platform, p. 309.) Elkania is an Obolus with the cardinal areas within the plane of the 

 margins of the valves. In the type species, Elkania desiderata (Billings), the area of the ventral 

 valve is entirely within the valve, while that of the dorsal valve has been nearly obliterated 

 in the process of change from an open backward-facing area to an inclosed forward-facing 



o The synonymy for this genus does not give a complete record of the various genera under which the species now included in Elkania were 

 formerly placed; it gives only those references in which the genus is discussed or described. To complete the record the following mere generic 

 references are listed: 



Obolella Billings [1862d, pp. 69 and 71]. I Obolella t Walcott [1884b, p. 67; 1886b, p. 111]. 



Obolella Davidson [1868, p. 309]. | 



62667°— VOL 51, pt 1—12 36 



