BRACHIOPODA. 411 
Leptena unicostata.] 
dental plates, are the distinct scars of the small adjustors. Surface marked by deli- 
cate, crowded papuille, strongest in front of the muscular area, and in the thin shells 
by the wrinkling of the outer surface. 
Dorsal valve nearly flat, with the anterior margin more or less reflexed down- 
ward. Cardinal area narrow, about one-third that of the other valve, with a broad 
and strongly convex chilidium. Dental sockets deep; crural plates slender, very 
oblique and merging into the median thickening, upon which is situated the small, 
bilobed, cordate cardinal process; in front of this is a short, low septum separating 
the small adductor scars; in the central portion of the valve there are three other 
inconspicuous septa. Just inside the outer margin of the valve is situated a prom- 
inent, rounded ridge of the same nature as that in L. rhomboidalis. 
L. charlotte differs from any other American species of Leptena in its zigzag, 
concentric, surface corrugations and in other minor features, which can be more 
readily seen in the illustration than by written comparisons. 
Formation and locality.—This species, in a dwarfed condition, is first met with in the upper portion 
of the Trenton limestone, and is not uncommon in the upper part of the middle third of the Trenton 
shales in the Bryozoa layers at Minneapolis and St. Paul, Minnesota. 
Collectors.—H. O. Ulrich and the writers. 
Mus. Reg. No. 8142. 
Leprana unicostata Meek and Worthen, sp. 
PLATE XXXII, FIGS. 6—9. 
1868. Strophomena unicostata MEEK and WORTHEN. Geological Survey of Illinois, vol. iii, p. 335 
1882. Strophomena unicostata EEA isel ies Geology of Wisconsin, vol. iv, p. 262, pl. xu, fig. 14. 
Original description: “Shell transversely subsemicircular, the greatest breadth 
being on the hinge margin, which terminates in rather acutely angular extremities; 
lateral margins generally nearly straight, or more or less concave in outline and 
converging from the extremities of the hinge to the front, which is rounded, a little 
straightened or slightly sinuous in the middle; geniculation of both valves from the 
ventral side, very abrupt all around the anterior and lateral margins to near the 
extremities of the hinge. Ventral valve almost perfectly flat [or slightly convex for 
a short distance anterior to the beak] and without any traces of concentric wrinkling 
on the disc between the hinge and geniculated front and lateral margins [in large 
Minnesota specimens there is more or less concentric wrinkling present in both 
valves, strongest along the cardinal line on each side of the beak and nearly obsolete 
medially]; beak very small or scarcely distinct from the cardinal margin and show- 
ing the usual minute [pedicle] perforation; area narrow, but a little wider than that 
of the other valve, and slightly arched and provided with a rather wider triangular 
fissure, closed by the convex deltidium [chilidium] and the cardinal process of the 
