Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/173

1869.] DAVIDSON—PEBBLE-BED BRACHIOPODA. 83 rous thread-like striae, which increase in number by the interpolation of one or two smaller striae between each pair of the principal. Dimensions variable. Length 5, width 6, depth 2 lines.

Although this shell was identified by Mr. Salter with Orthis redux (Barrande), both M. de Verneuil and myself entertain misgivings as to the correctness of the identification. The Bohemian Silurian species is not well known; the internal cast only has been figured by Barrande. It is a larger shell, and the median sinus is much deeper than what we find in our Budleigh examples. At any rate we have given to it the varietal designation of Budleighensis, which name can be hereafter retained as a specific one should the two shells be found to be specifically distinct. The correct identification of this species becomes very important, since no less than seven other forms have been found in the same pebbles with it. We therefore cannot determine at present whether it and its accompanying forms are of Silurian or of Devonian age.

24. Orthis Berthoisi, Rouault?, ''var. erratica'', Dav. Pl. V. figs. 13-16. Dav. Sil. Mon. p. 238, pi. xxxii. figs. 21-28.

This species has been fully described and illustrated at p. 233 of my Silurian Monograph. I cannot say whether it agrees with the Orthis Berthoisi, Rouault, as I have never seen the French type; nor can I say whether Mr. Sharpe was correct in identifying his Portuguese examples with Rouault's species. Budleigh specimens seem to resemble the Portuguese shell, while differing in some minor details; I have provisionally applied to them the varietal designation of erratica. Mr. Sharpe states that he obtained the fossil he identifies with O. Berthoisi from the lowest division of the Silurian system, at Portela de Loredo, in Portugal.

25. Orthis Valpyana, Dav. Pl. V. figs. 23-25. Sil. Mon. p. 235, pl. xxxii. figs. 29-33.

A description of this shell will be found in my Silurian Monograph. Mr. Vicary informs me that he believes that he has found it associated with O. Vicaryi in the same pebble. It appears also to bear some resemblance to O. Gervillei (Defr. & Barr.); but there is sufficient difference between the two forms to consider them specifically distinct.

26. Orthis pulvinata, Salter. Pl. V. figs. 17-19. Quart. Journ. Geol. Soc. vol. xx. p. 294, fig. 8, 1860. ?Porambonites, Salter, ibid. p. 295, pl. xvii. figs. 10-12.

Transversely oval; hinge-line shorter than the width of the shell; valves uniformly and moderately convex, surface marked by fine radiating lines or raised striae, increasing in number towards the margin by the interpolation of shorter striae. Area narrow. The internal cast of the ventral valve shows a large saucer-shaped muscular depression, divided in the middle by a widish convex ridge or space; in the internal cast of the dorsal valve there is a small oval slit,

G 2