1869.] DAVIDSON—PEBBLE-BED BRACHIOPODA. 81
ornamented with from sixteen to twenty simple angular ribs, of which
from three to six of the largest occupy the fold, while from two to
five furrow the sinus, the ribs on the lateral portions of the shell
being narrower. Length 9, breadth 10, depth 6 lines.
In size, shape, and character this shell entirely resembles R. inaurita,Sandberger. It is also not unlike R. daleidensis, Roemer, and R. livonica, v. Buch, but seems to be distinguishable from both by the shape and character of its mesial fold, which is regularly incurved, and not recurved upwards near the front as is the case with the last two species. R. inaurita occurs abundantly under the condition of internal casts and external impressions, and is associated with Sp. Verneuilii, R. Valpyana, Streptorhynchus crenistria, Productus Vicaryi, and Crania transversa. It is consequently a well-defined Devonian species, and as such it was identified by M. de Verneuil in 1863.
In his paper on the Budleigh-Salterton fossils Mr. Salter describes and figures a single internal cast of the dorsal valve of this species, as well as the cast of what he takes to be another species; but as the last-named specimen has been lost or mislaid, I could not examine it, and consequently cannot express any opinion with reference to its claims as a separate species. I will therefore simply reproduce Mr. Salter's description.
"Rhynchonella, sp.," Quart. Journ. Geol. Soc. vol. xx. p. 297, pl. xvii. fig. 14.
"A remarkable fossil, which, if it were more perfect, should receive a name. It is singularly inflated, both on tbe sides and in the great dorsal fold, which occupies one-half of the width, and is 7/10 inch long, and scarcely so wide, while the depth of the single dorsal valve we possess is 4/10. The shape is broad-ovate, the beak much pointed and rather produced, the sides arched, inflated, and separated by a rather broad depressed space from the raised sinus, which has four strong plaits. The sides are only faintly ribbed. The front is strongly incurved."
18. Rhynchonella elliptica, Schnurr? Pl. V. fig. 4.
Along with R. inaurita, another similarly shaped shell is occasionally met with, which may perhaps be an extreme variation in form of the last-named species, but may be distinguished from it by a greater number of ribs on the mesial fold. It is nearly circular, or a little broader than long, and ornamented with about twenty-eight ribs on each valve, of which nine occupy a slightly raised mesial fold. Length 8, width 8-1/2 lines.
This is certainly a Devonian species, as it occurs in the same boulders with R. inaurita and Spirifera Verneuilii; we have provisionally identified it with R. elliptica of Schnurr?
19. Rhynchonella, sp.? P1. V. figs. 5 & 6.
Of this species two internal casts have been found by Mr. Vicary; but, as no external impressions accompanied them, I dare not attempt their identification. In shape it is somewhat pentagonal, wider than VOL. XXVI.—PART I. G
