SHELLS OF THE AYMESTRY LIMESTONE. 



615 



Orthis orbicularis. (See PL 5. f. 16.) Also Upper Ludlow Rock. 



Loc. Botville, near Church Stretton. 

 Terebratula Wilsoni, f. 7 a. (M. C. t. 118. f. 3 ; Ter. lacimosa, Wahl. Balm. loc. cit. p. 139. 



t. 6. f. 1 ; Hisinger Petr. Suec. 80. t. xxiii. f. 3, not Linn. ; Ter. Wilsoni, Von Buch, Terebr. 



p. 47.) The form of the shell, approaching to cylindrical, and the long furrows upon the front 



sufficiently distinguish this species. 



Loc. Aymestry. This shell is highly characteristic of the central beds of the Ludlow forma- 

 tion and is of very constant occurrence in Salop, Hereford, Radnor, &c. 

 Terebratula Nucula. (See PI. 5. f. 20.) Also Upper Ludlow Rock. 



Loc. Aymestry, Ludlow, Sutton; Bottville, Caradoc. 

 Terebratula Navicula. (See PL 5. f. 17.) Also in the lowest bed of the Upper Ludlow Rock. 



These three species of Terebratula often mark the place of the Aymestry Limestone, as in 

 the Brecon anticlinal, the valley of Woolhope, at Usk, &c. 

 Loc. Aymestry, Ludloiv, Yeo Edge, and in numerous places. 

 Pentamerus Knightii, f. 8 a, b, c. (Min. Con. t. 28 ; Uncites Gryphoides, Defr., Ter. Gryphus, 

 Von Buch, p. 69 ; Gypidia Conchidium, Linn. Mus. Tessin. p. 90. t. 5. f. 8 ; Balm. loc. cit. 

 p. 125. t. 4. f. 1 ; Hisinger Petr. Suec. 71 L t. xxi. f. 10; Anomia bilocularis Hisinger 

 Act. Holm. 1798. p. 285.) After the examination of a great number of specimens it has been 

 ascertained that the lesser valve varies much in convexity, and hence that P. Aylesfordii, Min. 

 Con. t. 29, is not a distinct species. (See f. 8 c.) 



The Pentamerus Knightii presents the peculiar organization by which the genus is marked 

 in a high degree of perfection ; the lesser valve being divided internally by two longitudinal, 

 parallel, approximate septa, and the other valve by one large, also longitudinal, septum, which 

 is forked towards the beak. These septa are composed of short fibres which meet in the middle, 

 so that each septum is easily divided into two. Owing to this structure and to its usually 

 being filled with subcrystalline carbonate of lime, this fossil, though sometimes entire, fre- 

 quently splits into two parts, one containing two and the other three of the chambers formed 

 by the septa : commonly also, a small piece separates from within the forked part of the large 

 septum near the beak. (See f. 8 b.) 



The Pentamerus Knightii may be seen in this state all along the escarpments of the 

 Ludlow formation, extending from Aymestry to the View Edge west of Ludlow. Throughout 

 that district and at Sedgeley near Dudley, this species of Pentamerus is peculiar to the 

 Aymestry Limestone, though one example of it has been observed (by Mr. Davies of Presteign) 

 in the equivalent of the Wenlock Limestone near Presteign. (See p. 313.) 



The name of Mr. Thomas Andrew Knight, F.R.S., President of the Horticultural Society 

 of London, in whose beautiful demesne of Downton Castle it is found abundantly, has been 

 with great propriety attached to this curious and characteristic fossil. 

 Loc. Aymestry j Bownton on the Rock ; Yeo Edge ; and Sedgeley, Staffordshire. 

 Lingula Lewisii, f. 9. Oblong, compressed, smooth ; sides straight and parallel. Length 1 inch 

 2 lines, width 9| lines. The squareness of the outline produced by the straight sides is cha- 

 racteristic. 



Loc. Aymestry and many situations in the Ludlow promontory, viz. Mary Knoll, Sunny 

 Bank, Palmer's Cairn ; also at Abberley and at Sedgeley ; very characteristic. 

 This large and beautiful species, of which the shell is generally well preserved and often 



of a blue colour, is named after the Rev. T. T. Lewis of Aymestry, 



4 1 2 



