80 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Dec. 8,
form—some examples being almost circular, while others are transversely
oval. N. Vicaryi is not rare in certain pebbles, no less
than thirty-five specimens, representing different ages, having been
found by Mr. Vicary. It bears also some resemblance to N. ventricosa,
Hall, and is probably of Silurian age, for it has been found
associated with impressions of an Orthis much resembling O. redux.
In America N. elegans belongs to the Lower Helderberg rocks. An
allied form N. (S.) pisum, Sow., is not rare in our British Upper
Silurian strata.
14. Athyris incerta, n. sp.? P1. IV. fig. 12.
More or less pentagonal, rather wider than long; dorsal valve moderately convex; surface smooth, with a broad, slightly produced mesial fold, flattened or depressed along the middle; ventral valve convex; sinus shallow. Length 6, width 8 lines.
Of this species only one or two internal casts of the dorsal valve and an external impression have been met with by Mr. Vicary; it is therefore impossible, with such scanty materials, to even hint at a definite specific identification. It much resembles certain small Devonian specimens of A. concentrica, and also the Carboniferous A. ambigua, Sow. Some indeterminable impressions of an Orthis and of Tentaculites have been found along with it in the same pebble.
Internal casts of two more species, perhaps referable to this genus, have been found. They are not, however, sufficiently complete to admit of being specifically determined; but, for the sake of reference, I must give them a provisional denomination.
15. Athyris? budleighensis, n. sp.? Pl. IV. fig. 14.
Of this species the internal cast of a ventral valve has alone been discovered; it is almost circular, slightly wider than long—no markings being observable but two slits in the beak, due to dental plates. It measures, length 9, and width 9-1/2 lines, and was found by Mr. Vicary along with Spirifera Verneuilii and Rhynchonella inaurita. It is consequently a Devonian species.
16. Athyris? erratica, n. sp. Pl. IV. fig. 13.
Shell small, elongated, oval; valves moderately convex. Length 4, width 3, depth 2 lines.
The internal cast of one specimen was found by Mr. Vicary; we are not acquainted with its exterior.
17. Rhynchonella inaurita (Sandberger). P1. V. figs. 1-3. Brach. rheinischen Schicht. in Nassau, p. 41, p1. xxxiii. fig. 5, 1855. Rhynchonella?, Salter, Quart. Journ. Geol. Soc. vol. xx. p. 296, p1. xvii. fig. 15.
Subtrigonal, wider than long, both valves convex; dorsal valve gibbous; mesial fold rising abruptly with greater or less width, and forming in profile a regular convex curve. In the ventral valve the sinus is broad and moderately deep, extending from the extremity of the beak to the front; beak incurved. Surface of each valve
