BRACHIOPODA. 341 



Llngala era.l 



attachment of the muscular walls of the perivisceral chamber has not been detected, 

 unless it be combined with the scar of the posterior branches of the pallial sinuses, 

 which really seems to be the case. If this is so, the posterior branches of the sinuses 

 can have had ramifications on but one side instead of on both, as in the case of L. 

 anatina. This would be a marked specific but not a generic character." 



There is considerable variation in the outline of this species, some being short 

 and wide, while others are long and comparatively narrow. Specimens with the 

 shell adhering to the limestone show that the valves near the edges are considerably 

 flattened, giving the shell a greater width than the casts of the interior indicate. 

 These specimens greatly resemble L. quadrata, as figured by professor Hall (Pal. New 

 York, vol. i, pi. LXXIX, figs. la. Ib), and in several cases we have seen the species 

 labeled in this way. L. elderi can be distinguished readily from that species by 

 the absence of a well-developed median septum in the interior of the dorsal valve. 

 In L. quadrata Hall=L. rectilateralis Emmons, the septum is usually indicated 

 externally by a strong central depression. By washing and picking away the 

 adhering portion of the shell, casts of the interior of L. elderi Whitfield, can be 

 made to show the muscular scars, and the delicate detail of the ramification of the 

 vascular trunks. 



Formation and locality. Common in the Trenton limestone at Minneapolis, Wanamingo, Oxford 

 Mills, Fountain, and Rochester, Minnesota; Beloit, Wisconsin. A single example of this species was also 

 found near the base of the Galena* shales on St. Anthony Hill, in the city of St. Paul, Minnesota. In the 

 Salmon River or Cincinnati group at Cincinnati, Ohio, and at Covington, Kentucky. 



Collectors W. D. Hurlbut, Wm. Howling, C. L. Herrick, H. V. Winchell, W. H. Scofleld, and the 

 writers. 



Mus. Reg. Nos. 291, 786, 3499-3503, 5009, 5010, 5061, 5133, -5668. 



LINGULA EVA Billings. 



PLATE XXIX, FIGS 5 and 6. 



1861. Lingula eva BILLINGS. Canadian Naturalist and Geologist, vol. vi, p. 150. 

 1863. Lingula eva BILLINGS. Geology of Canada, p. 141, flg. 73. 



Original description: "Shell from one to one and a half inches in length, 

 greatest width near the front margin, thence gradually tapering with nearly 

 straight sides until within one-fourth of the length from the beak, from which point 

 the sides rapidly converge to the beak; apical angle about 90; both valves rather 

 convex along the middle, thence descending with a flat or gently convex slope to 

 the sides and front margin. Surface with distinct sub-imbricating concentric 

 ridges and fine striae, and when partially exfoliated obscure longitudinal striae are 

 visible. 



*For a definition of this and other stratigraphic terms consult the introductory chapter. 



