SHELLS OF THE LOWER SILURIAN ROCKS. 



643 



Lituites? Cornu-arietis {a), PI. 20. f. 20. Discoid ; whorls about 4, close, crossed by numerous, 

 oblique, sharp, slightly raised costse, mixed with lines of growth. Diameter nearly 2 inches. 

 Loc. Corton, Presteign. 



Lituites Cornu-arietis (/3), PI. 22. f. 18. This differs from var. a only in having the costae more 

 distant and regular. Diameter nearly 2 inches. 



Loc. Cefn-y-garreg, near Llandovery, in black schistose beds of passage from the Silurian 

 into the Cambrian Hocks, 

 Bellerophon trilobatus, var. ?, PI. 3. f. 16. (In the upper beds of Caradoc Sandstone.) 



Loc. Eastnor Park; Michaelwood Chase (with Pentamerus Icevis) ; north-east of Gaerfawr; 

 Prescoed Common, Usk. 

 Bellerophon acutus, PI. 19. f. 14. Compressed, smooth, umbilicated; whorls keel-shaped, acute ; 

 umbilicus broad ; aperture triangular, longer than wide. Diameter nearly i an inch, width of 

 aperture about 2 lines. 



Loc. Horderley . (In the upper beds of Caradoc Sandstone.) 

 Bellerophon bilobatus, PI. 19. f. 13. Nearly globose, smooth; aperture two-lobed. Diameter- 

 \\ inch, width of aperture 1 inch 3 lines. 



Loc. Horderley and Wistanstow ; Welch Pool ; Michaelwood Chase; Tortworth ; Benvyns. 

 Tentaculites scalaris, PI. 19. f. 15. (Schloth. Pet. t. xxix. f. 9 b.) Subulate, composed of a series 

 of truncated cones ; internal cast of the same form, but even towards the apex. Diameter 1 line. 



The truncated cones of which this appears to be formed have their bases directed towards 

 the apex of the shell ; so forming a set of steps rather than rings, like the sliding joints of an 

 opera-glass. 



It is not possible to distinguish this body from the Tentaculites of the Ludlow formation, 

 though it is much more abundant in the Caradoc Sandstone or Upper Member of the Lower 

 Silurian Rocks. 



Loc. South of the Bogmine, Shelve ; Eastnor Park ; Damory Hill, Tortivorth. 

 Tentaculites annulatus, PI. 19- f. 16. {Schloth. Petr. t. xxix. f. 8 Cyathocrinites pinnatus 

 {Brachia auxiliaria), Goldfuss, vol. i. p. 190. t. lviii. f. 7 h £.) Subulate, ornamented with 

 rounded rings placed at regular distances ; the spaces between them smooth ; the interior of the 

 same form as the outside. Diameter 1^ lines. 



(In the upper beds of Caradoc Sandstone.) 

 Loc. East flank of the Caradoc; Hope Mill, near Shelve ; Michaelwood Chase, Tortivorth. 



The generic names of Leptcena, Atrypa, and Orthis, being new to English geologists, their use 

 on this occasion demands an explanation. They are, in fact, subdivisions of the great family of Te- 

 rebratula, which, having been established by Dalman, have been since adopted by many foreign 

 authors ; and Mr. J. de C. Sowerby gives the following reasons for sanctioning their introduction 

 among us. 



"The generic names Leptana, Atrypa, and Orthis, have been adopted from Dalman' s memoirs 

 in the Stockholm Transactions, in deference to the opinion of that author. The first of these 

 synonyms (derived from Xstttos) stands in the place of Producta or Productus, a name to which 

 grammarians have objected. 



