. A dictionary of the fossils of Pennsylvania and neighboring states named in the reports and catalogues of the survey ... Paleontology. 891 Rhyn. ruptly rounding, and at the base produced in a slight exten- sion. Ventral valve depressed convex, slightly gibbous at about one-third the length from the apex, curving abruptly to the cardinal and antero-basal margins, more gradually to the lower lateral margins, becoming depressed in a shallow sinus, which commences at about one third to one-half the length from the beak; beak slightly incurved, strongly projecting be- yond the beak of the opposit
. A dictionary of the fossils of Pennsylvania and neighboring states named in the reports and catalogues of the survey ... Paleontology. 891 Rhyn. ruptly rounding, and at the base produced in a slight exten- sion. Ventral valve depressed convex, slightly gibbous at about one-third the length from the apex, curving abruptly to the cardinal and antero-basal margins, more gradually to the lower lateral margins, becoming depressed in a shallow sinus, which commences at about one third to one-half the length from the beak; beak slightly incurved, strongly projecting be- yond the beak of the opposite valve. Dorsal valve convex, greatest convexity at or a little below the middle, gradually curving to the apex and cardinal margins, more abruptly to the lateral margins; mesial fold commencing at a little above the middle and often becoming prominent at the front; beak small and nearly straight. Surface marked by from ten to twelve rounded or subangnlar plications, which become obsolete on the upper portions of the valves. The mesial fold is composed of three plications much more prominent than the others. In the sinus there are three plications smaller than the others; the two plications bordering the sinus larger than tho?e on the other portions of the shell. The specimens ob- served have a length of 9 or 10 mm., and a width of from 7 to 9 mm.; a transverse section broadly oval, having a width of 5 or 6 mm. This species is easily distinguished from any other of this formation at present known. The outline is very sim- ilar to some of the forms of U. {Stenocisma) eximia^ of the Chemung group, but the shell is smaller, the plications of the fold and sinus are fewer and the plications become obsolete on the upper half of the valve. Clinton, Vh. Rhynchonella laticostata. For Hgures see under Atrypa laticostata^ where they are wrongly so named. (R. P. W., 1889.) Rhynchonella ? laura, Billings. (A synonym for liei- orhynchus multi- costus. S. A. Miller) Geology of Canada, 1863, p
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