Scientia Sinica

No. 1 . WANG: NEW SPECIES OF BRACHIOPODS [I] 173

line; cardinal extremities obtuse; very unequally biconvex in lateral profile, greatest thickness in the anterior margin; anterior commissure strongly uniplicate.

Ventral valve very shallow, flatly convex, postero-lateral margins sloping abruptly toward the cardinal line; lateral flanks moderately convex; median portion depressed anteriorly to form a broad and shallow sulcus with a flat bottom, and geniculated in right angle to meet the dorsal fold; lingual extension quadrate and long; umbo narrowly and gently arched; beak small, incurved against that of the dorsal valve.

Dorsal valve very strongly convex, more than four times the thickness of the ventral valve; surface curving from median portion rapidly to the beak and flattening thence toward the anterior margin; flanks sloping abruptly from borders of the fold to lateral margins, almost making a right angle with the plane of commissure; fold low, narrower than the sulcus, gently convex, developed only in the anterior part of the valve; umbo narrowly convex; beak minute, incurved, hidden under the ventral beak.

External surface ornamented with simple, low, rounded plications, 9 in sulcus, 8 on fold, and 16 or more on each lateral flank; interspace about as wide as the plication.

Dimensions (mm): Length 27.3; width 28.8; thickness 27.0. Holotype, I.P.A.S. 8016.

Horizon and locality: Lungkouchung Bed, Middle Devonian; Lungkouchung Village, Hsianghsiang District, Hunan Province.

Collector: K. K. Chao. .

Discussion: This species is distinguished by its large size, its sharp and obvious surface ornamentations with its prominent sulcus extending dorsoward into a long quadrate prolongation, the greatest thickness of the shell being thus in the anterior margin.

In regard to the large size and cuboidal outline, this new species appears to be allied to Hypothyridina obesa Grabau'! from northern Szechwan Province. It differs, however, in having a width greater than length, in having a less convexity in the posterior portion of the dorsal valve, and in having a much narrower fold and sulcus with a relatively longer lingual extension.

Furthermore, the flattened rather than rounded surface plications and the linear interspaces of Hypothyridina obesa also serve to distinguish it from the present form.

Hypothyridina linglingensis Wang (sp. nov.) (PIS IM, G5 Figs: 15) =

Size small for the genus; subcuboidal in shape, rectangular in outline,