SHELLS OF THE LOWER SILURIAN ROCKS. 



637 



We have only seen casts of portions near the beak of this shell, but there is enough to show 

 that it must have been very heavy. F. 1 b. probably indicates a variety with irregular cells 

 rather than furrows. Diameter about If inch. 



This and the following figure belong to the lowest beds of the Silurian System. 

 Loc. Cefn Rhyddan ; Caermart hens hire. 

 Atrypa undata, PI. 21. f. 2. Transversely elliptical, gibbose, smooth; an elevation along the 

 middle leads to a tongue-shaped sinus in the edge of one valve, and a corresponding projection 

 in the other. Length 10 lines, width 1 inch 4 lines. 



Loc. Cefn Rhyddan, Llandovery ; west side of Cefn-y -Garreg, Llandovery; Robeston 

 Wathen, Pembrokeshire. 

 Atrypa Lens, PL 21. f. 3. Suborbicular, depressed, smooth, obscurely radiated, elevated along the 

 middle of the upper valve. Length nearly 2| inches, width about 2 inches. 

 Loc. North end of Snead's Heath {Lickey Quartz) ; Mandinam and Cefn Rhyddan, Llan- 

 dovery. 



Atrypa plana, PI. 21. f. 4. Orbicular, with the front rather produced, flattened, smooth. Length 



about 7 lines, width 8 lines. 



Loc. Tynewidd, Llandovery. 

 Atrypa globosa, PI. 22. f. 2 b. Globose, obscurely channelled, smooth. Diameter about 6 lines. 



Loc. Castell Craig, Gwyddon ; and Gorlhvyn-fach, Caermart -hens hire. 

 Atrypa poly gramma, PI. 21 . f . 4 a. Transversely obovate, finely radiated, valves unequally convex, 



the lower with a wide, shallow canal along the middle; radii increasing in number towards the 



margin. Length 1 inch, width 1 inch. 



Loc. Powis Castle. 



Atrypa orbicularis, PI. 19. f. 3 and 4. Suborbicular, rather wider than long, with a slight sinus 

 in the front, furrowed ; furrows numerous, forked, the ridges between them not scaly ; valves 

 equal. Length 7 lines, width 8 lines. 



Much resembling A. aspera, but smoother. 

 Loc. Gorllwyn-fach (f. 1.); Conygree Coppice (f. 4.); Woodford Hill, Abberley j Malvern 



Ridge, End Hill. 



Atrypa hemisphcerica, PI. 20. f . 7. Almost orbicular with the back nearly straight, radiated ; radii 



about 12, angular; valves unequal, one hemispherical, the other nearly flat. Length 4 lines, 



5 lines. 

 A beautiful fan-like shell. 



Loc. Ankerdine Hill, Worcestershire ; Damory Hill, Michaelwood Chace, Gloucestershire. 

 Atrypa ajjinis, PI. 6. f. 5. Ranges from the Aymestry Limestone to the upper beds of the Ca- 



radoc Sand'stone. 



Loc. Cefn, Welch Pool to the Breiddens ; Tynewidd; Golden Grove; Marloes Bay, Pem- 

 brokeshire ; Lower Lickey [overlying beds). 

 AtrypcB, PI. 22. figs. 3, 4 and 5. These are curious casts of different valves, but so much distorted 



that we cannot determine their general form, nor even say whether or not they belong to the 



same species. Figs. 4 and 5 are two views of one specimen. 



Loc. Marloes Bay, Pembrokeshire. 

 Spirifer radiatus, PI. 12. f. 6. Ranges from the Wenlock Limestone to the upper beds of the Ca- 



radoc formation. 



Loc. Gaer favor, Guilsjield ; Lower Lickey [overlying beds). 



