FOSSIL SHELLS OF THE OLD RED SANDSTONE. 



603 



Area ? Transversely oblong, very convex; muscular impressions very deep. Too 



imperfect to figure or to name ; it is not very unlike A. Eastnori of the Caradoc sand- 

 stone. 



Avicula rectangularis, f. 2. Subtriangular, very convex, approaching to carinated, smooth; an- 

 terior side nearly straight, at a right angle with the equally long hinge line ; front rounded; 

 posterior side slightly projecting in form of a large lobe; length 1 inch 2 lines, width the same. 

 Loc. Horeb Chapel. 



*Leptama lata, figs. 10 b and 12 c. This is one of the most characteristic shells of the Upper 



Ludlow Rock, (see PI. V. f. 13.) 



Loc. Felindre. Horeb Chapel. 

 *Spirifer ptychodes, f. 13. [Belthyris Dalm. Act. Holm., 1827, P- 124. t. 3. f. 5 ; Hising, Petr. 



Suec. p. 73. t. 21. f. 8.) Slightly elongated, smooth, with 5 rounded plaits ; beak of the larger 



valve prominent, curved; length 3| lines, width about the same. 



Loc. Felindre. Also in Upper Ludlow Bocks. 

 *Orthis lunata, f. 12 c?,; also in the Upper Ludlow Rock. (See PI. 5. f. 16 and description.) 



Loc. Horeb Chapel. 



*Terebratula Nucula, f . 1 c and 12 g. Abundant in the Upper Ludlow Rock. (See description 

 PI. 5. f. 20.) 



Loc. Horeb Chapel. Felindre. 

 Lingvla cornea, f. 3. Compressed, oblong, rectangular, nearly half as long again as wide; texture 



approaching horny; length 7 lines, width 5 lines. 



Loc. Tin Mill, Downton, Ludlow. 

 Natica glaucinoides, f. 14. Small, globose, with a closed umbilicus : very like the N. glaucinoides, 



M.C., when young ; width about 3 lines. 



Loc. Felindre. 



*Trochus helicites, tie and 5. Depressed, smooth, convex beneath; , whorls about 4, hardly con- 

 vex above (except in the cast), obtusely angular at the margin of the base ; umbilicus small 

 and deep ; width from \ inch to nearly 1 inch. 



The large specimen, f. 5, is rather more angular about the margin; f. le* shows the iinpres- 

 sion of the outer surface. 



Loc. Horeb Chapel. Also in Upper Ludlow Rock. 

 Turbo Williamsi, f. 6. Conical, smooth; whorls convex, about 4; base convex, with a narrow 

 umbilicus ; aperture round; height If inch, width 1^ inch. 1 

 Loc. Horeb Chapel. 



Turritella obsoleta, i.^a and 12 /. Subulate, elongated, smooth ; whorls 9, convex; aperture round; 



length \\ inch, width 5 lines. Variable in size ; the measures given are of the largest specimen. 



Loc. Horeb Chapel. Felindre. 

 Turritella gregaria, f. If. Subulate, smooth, whorls 6, convex; aperture round; length 4 to 6 



lines, width 2 to 3 lines. Many individuals of this Turritella occur together, and mostly of 



one size ; it may nevertheless possibly be the young of the last species. 



Loc. Horeb Chapel. 



1 I have named this shell after my friend Mr. Williams of Llandovery, who has materially enriched this work 

 by collecting fossils. (See p. 350.)— R. I- M. 



