: BRACHIOPODA. 417 
Orthide .] 
margin, where they become obsolete. The depression between this ridge and the 
outer elevated margin of the muscular area is granulose, while the slope on the 
outer side of the former is quite abrupt. 
This small species of Plectambonites is quite distinct from all other American 
forms. The convexity of the shell, surface ornametation and the interior char- 
acters of the dorsal valve will distinguish it at once from P. sericea Sowerby and 
P. decipiens Billings. Its relationship is yather with the latter species, on account 
of the sharp elevation just inside the margin of the dorsal valve. P. gibbosa seems 
to be closely allied to P. quinquecostata McCoy,* but until more is known of the 
interior characters of the latter further comparisons are impossible. That species 
is found in the Caradoc and Llandovery of England; also in Scotland, Ireland and 
Russia. 
Formation and locality —Not uncommon in the Galena at several localities in Goodhue county; also 
at Mantorville and Old Concord, Minnesota. 
Collectors.—M. W. Harringtop, A. D. Meeds, W. H. Scofield, E. O. Ulrich and the writers. 
Mus. Reg. Nos. 147, 423, 8165, 8166. 
Family ORTHIDA, Woodward. 
Genus ORTHIS, Dalman, emend Hall. 
1828. Orthis, DALMAN. Kongl. Vet. Acad.-Hand., pp. 93, 96. 
1892. Orthis, HALL. Palzeontology of New York, vol. viii, pt. i, p. 192. 
Description: “The distinguishing features of these shells are the plano-convex 
contour; the strong, sharp and comparatively few coste, rarely, if ever, bifurcating; 
the elevated and somewhat incurved cardinal area on the pedicle valve; the relatively 
slight development of the dental lamella, which do not extend the entire length of 
the umbonal cavity. The cardinal process on the brachial valve is af elongate, 
vertical plate, extending from the apex the whole length of the delthyrium, thus 
longitudinally dividing the deep deltidial cavity. It is usually simple, both on the 
outer edge and at its distal extremity. 
“In this group of orthids [ Orthis restricted], more frequently than elsewhere, we 
find a character rarely developed in any stage of growth, viz: the existence of a 
transverse apical plate in the delthyrium of the pedicle valve [the rudiments of a 
deltidium]. 5 ns The greatest development attained by this feature, in 
any of the numerous species of Orthis studied, is to be found in 0. tricenaria of the 
Trenton and Hudson River faunas; it has also been observed in 0. calligramma, var. 
davidsoni, although it does not appear in any of the figures of this species and its 
varieties given by Mr. Davidson, nor is any mention made of it in his descriptions. Its 
*Sil. Foss, Ireland, p. 33, pl. m1. fig. 8, 1846; and Davidson’s Mono. British Sil. Brach., p. 322, pl. xLvi, figs. 28-27. 
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