SHELLS OF THE UPPER LUDLOW ROCK. 



611 



N.B. This fossil has been figured in this plate inadvertently, for it does not belong to the 

 Upper Ludlow, but rather to the Lower Ludlow and Wenlock strata. 

 Orthis lunata, f. 15. Transversely obovate ; finely and deeply striated; valves almost equally con- 

 vex ; the lesser with a slight depression along the middle ; beaks not very prominent, and 

 within it has two semicircular ridges; area of the hinge small. Length 5 lines, width 7 

 lines. 



Loc. Ludlow ; Delbury ; of very frequent occurrence ; also in the lowest beds of Old Red 

 Sandstone. 



Orthis orbicularis, f. 16. Obovate, approaching to orbicular ; finely and deeply striated ; the larger 

 valve very convex, with a slighly curved beak, within which is a straight longitudinal ridge, with 

 a curved one on each side of it (seen best in the impressions they leave in the cast) ; the other 

 valve slightly convex with a wide depression along the middle ; area of the hinge very small. 

 Length 6 lines, width 7 lines. 



Loc. Ludlow; Delhury; Sutton, near Wenlock; Dog Hill, near Ledbury ; Cwm-nant- 

 gwyn, near Builth. 



These two species of Orthis are so nearly alike, that it is often impossible to determine to 

 which the specimen under examination may belong, unless it be very perfect, or show the im- 

 pressions upon the cast of the characteristic ridges in the interior. One or both species occur 

 with Leptcena lata and Terebratula Nucula in numberless localities near Ludlow, Munslow, 

 Aymestry, Presteign, Knighton, Kington, Builth, Brecon (the Corn-y-fan, or Brecon anti- 

 clinal), Usk, Sedgeley, Abberley and Ledbury. 

 Terebratula Navicula, f. 17- Oblong, boat-shaped, smooth; the upper valve nearly flat, its sides 

 elevated, the front depressed; the lower valve obtusely keeled, its beak short, incurved: f. \*J a 

 represents the cast of the interior. Length 7 lines, width 5 lines. 



Loc. Ludlow promontory ; Clyro Hills , Radnorshire ; Brecon anticlinal, viz., Corn-y-fan; 

 Alltfawr and Rhiwannest, abundant, at the base of the Upper Ludlow. 

 Terebratula canalis, f. 18. Elliptical, smooth, with a narrow longitudinal furrow; front emarginate ; 

 beak incurved. Length \ an inch, width 4^ lines. 



Our description of this is necessarily meagre, because we have only seen one valve. The 

 fossil belongs rather to the Lower Ludlow. 

 Loc. Near Usk. 



Terebratula lacunosa, f. 19. (Anomia lacUnosa, Linn. ; Gmel. t. i. 3343. Terebratulites lacu- 

 nosus, var. Schlotheim, Nachtrage, zur Petrefact. p. 68. t. 20. f. 6 ; Ter. borealis, Von 

 Buck. loc. ext. p. 67; von Hisinger.) Obovate, gibbose, obscurely 3 lobed, acutely plaited; 

 plaits about 16, 4 or 5 of which in the middle of the front are much elevated; beak small, 

 pointed, slightly incurved. Length 7 lines, width 8 lines. 



This is one of the least lobed varieties of T. lacunosa, if it be a variety of that species ; the 

 specimens before us are not complete enough to determine a question so difficult in this section 

 of the family of Terebratulce, 



Loc. Ludlow promontory and Delbury, Salop ; Aram, near Neivnham ; Trewerne Hills ; 

 the Maund, Abhereddw, and Pain's Castle, Radnorshire ; Abberley Hills. 

 * Terebratula Nucula, f. 20. Globose, obscurely 3 lobed, plaited; plaits sharp, about 15, 3 or 4 

 of which are prominent and elevated in the middle of the front ; beak small, adpressed ; lower 

 valve slightly flattened. Length 5 lines, width the same. 



Loc. Ludlow; Delbury; Presteign; Ledbury; Bagbarrow Hill; and west of Malvern 



