620 



SHELLS OF THE LOWER LUDLOW ROCK, 



Orthoceras eccentricum f Also Wenlock Shale. (See PI. 13. f. 16.) 

 Loc. Trefnant, Montgomeryshire ; in black calcareous nodules. 



Orthoceras imbricatum, PI. 9. f. 2. {Orthoceratites imbricatus, « Wahl." Hising. Petr. Suec. 

 p. 29. t. ix. f. 9 ?) Gradually tapering; septa very near, waved. 



We have not been able to discover the position of the siphuncle in the shell before us. It 

 resembles O. undulatum of M. C. t. 59. in the curvature of the septa, but is more gradually 

 tapering in form, and has not so much tendency to enlarge in the last chamber, and to contract 

 again towards the aperture, which gives the O. undulatum a fusiform aspect ; it agrees better 

 with O. imbricatus of Wahlenberg and Hisinger, which perhaps differs from O. undulatum 

 M. C, in the position of the siphon. The O. undulatus of Hisinger is O. annulatum of M. C, 

 and his O. annulatus is probably our O. Ibex, for he describes it smooth, in which it differs 

 from O. annulatum. 



This specimen is much flattened, perhaps by pressure. 

 Loc. Ludlow escarp?nents. 



Orthoceras Jilosum, PI. 9. f. 3. Rather quickly tapering, longitudinally ribbed ; ribs fine, numerous ; 

 septa numerous. 



This differs from O. striatum of M. C. in the coarseness of the lines upon the surface, which 

 in this are sharp elevations. The position of the siphon is unknown ; length 1| foot, greatest 

 width about 4 inches. 

 Loc. Ludlow escarpments. 

 Orthoceras virgatum, PI. 9. f. 4. Subfusiform, elongated, longitudinally and irregularly but not 

 deeply fluted, grooves 40 j septa numerous ; length 6 or more inches, diameter one inch and a 

 half. 



Nearly like O. Gesneri of Martin t. 38 ; but it has smaller and less regular grooves, and is 

 rather fusiform. O. angulatus of Wahlenberg (Hisinger) is curved but is apparently O. Ges- 

 neri of Martin, and O. circularis M. C. is a worn specimen of the same. 

 Loc. Mo cktree Forest ; Abberley Hills. 



Orthoceras dimidiatum, PI. 8. f. 18. Slender; surface transversely undulated, waves reaching 

 only half across; septa moderately distant; length 21 inches, diameter ^ inch. 

 Loc. Water -break-its-neck, Radnor Forest. 



Orthoceras Jimbriatum. (See PI. 13. f. 20.) Also Wenlock shale. 



Orthoceras annulatum, PI. 9. f. 5. 



This also occurs in the Wenlock shale, and is described hereafter. 



Orthoceras Ibex. (See PI. 5. f. 30.) Also Upper Ludlow Rock. 

 Loc. Near Ludloiv and Western jianks of the Malvern Hills. 



Orthoceras pyriforme, PI. 8. f. 19, 20. Ovato pyriform, smooth, the chambered portion elongated ; 

 septa numerous, even ; siphuncle half way between the centre and margin, rather large, in- 

 flated between the septa ; aperture narrow, enlarged at one extremity where the edge is re- 

 flected. Length of inflated portion 4 inches, diameter of ditto 2\ inches. 



The last chamber occupies half the ovate portion of the shell, and varies in shape according 

 to the direction of the pressure. The form of the aperture, as far as can be collected from 

 the imperfect specimens in our hands, is curious, being very narrow for about half an inch, 

 and then expanded to circular ; the edge is reflected, especially at the larger end of the aper- 

 ture, where it resembles the beak of a pitcher. This remarkable shell thus forms a link 

 between Orthoceras and Phragmoceras, differing from the latter only in being straight. Were 



