imACHIOPODA. 341 
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 beinj^ 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. 16), 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 BUUngs. 
PLATE XXIX, PIGS 5 and 6. 
1861. Lingula eva Billings. Canadian Naturalist and Geologist, vol. vi, p. 150. 
1863. Lingula eva Billings. Geology of Canada, p. 141, fig. 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 strite are 
visible. 
* For a definition of this and otlier stratigraphic terms consult the introductory chapter. 
