640 



SHELLS OF THE LOWER SILURIAN ROCKS, 



Orthis lata, PL 22. f. 10. Semicylindrical, rather straight in front, depressed, radiated ; radii 



linear, unequal in thickness, Length 5 lines ; width 9 lines. 



This much resembles Leptana lata, but both valves are convex, the radii unequal in size, 



and there are no spines upon the hinge line. 



Loc. Gorllwyn and Goleugoed, Caermart hens hire ; Berwyns. 

 Orthis triangularis, PI. 20. f. 17. Triangular, rounded in front, convex, finely radiated. Length 



4| lines ; width 5 lines. Found in Volcanic Grit. 



Loc. Marrington Dingle, near Chirbury. 

 Orthis canalis, PI. 20. f. 8., & PI. 13. f. 7 b. Also Wenlock shale. 



We have here figured casts of the interior, to show how they differ from the allied species 



in the higher beds of the Upper Silurian Rocks. The specimens are larger than those in the 



Wenlock shale. 



Loc. In Caradoc Sandsto?ie at Horderley and Whittingslow , near the Caradoc ; Moel-y- 

 garth and Gaerfawr, near Welchpool. In Llandeilo Flags at Clog-y-frain ; Golden 

 Grove, Caermart henshire ; and at Lla?npeter-felfrey, Pembrokeshire. 

 Orthis testudinaria? Dalman, PI. 20. f. 9. {Balm. I. c. p. 115. t. ii. f. 4. His. Pet. Suec, p. 70. 



t. xx. f. 11.) Nearly orbicular, with a straight back, radii numerous, unequal in length, 



granulated ; larger (upper) valve very convex, approaching conical, with an incurved beak; 



the other slightly convex, with a depression along the middle ; hinge line nearly as wide as 



the shell. Length 6^ lines ; width 8 lines. 



Orthis canalis differs from this in being less convex and more finely radiated; the internal 



structure is also different. 



Loc. Gaerfawr, Guilfield and Moel-y -garth ; east and south of the Caradoc, abundant ; also 

 at Powis Castle ; Mandinam and Golden Grove. 

 Orthis bilobata, PI, 19. f. 7- Transversely obovate with a straight back ; covered by thin irregular 

 radiating ridges ; upper valve concave, with a broad angular elevation along the middle ; lower 

 valve very convex, with a deep broad channel along the middle; sides a little produced 

 towards the extremities of the hinge line, rounded. Length 1 inch 2 lines ; width about 1 inch 

 7 lines. 



Loc. Acton Scott, Horderley ; and also in the Upper Cambrian Rocks of Bala. 

 Orthis Vespertilio, PL 20. f. 11. Transversely obovate elongated, with a straight back, covered by 

 thin irregular radiating ridges ; upper valve slightly convex, with a broad angular elevation 

 along the middle ; lower valve convex, with a deep broad channel along the middle ; sides 

 angular at the extremities of the hinge line. Length f inch; width 1 inch 2 lines. 



A less convex shell than the last, but in many points strongly resembling it. 

 Loc. From Gorton near Clunbury , along the south-east flank of the Caradoc ; Acton Burnett 

 and Stevens Hill, Coundj the Maen, Meifod; Trilobite Dingle, Welch-Pool ; in Llan- 

 deilo Flags, Caermarthenshire ; and in the Cambrian Rocks of Bala. 

 Terebratula furcata, PI. 21. f. 16. Orbicular, very convex, smooth; beak of one valve much 

 curved ; interior marked with several furrows, and a forked channel in the middle. Length 

 and width 4 lines. 



Loc. S. of Bogmine in the Corndon Hills ; {Caradoc Sandstone.) . 

 Terebratula unguis, PI. 21. f. 13. Orbicular, very convex, plaited; plaits about 12, sharp and 

 large ; beak incurved. Length 5| lines ; width 5 lines. 

 Loc. Horderley; Cefn near Welchpool {Caradoc). 



