132 



BRITISH STirRIAX BRACHIOPODA. 



As we have already remarked, this shell is extremely variable in the number of its 

 longitudinal striae, as well as in that of the number and length of its concentric foUaceous 

 expansions. At the request of Prof. Edward Forbes, ^Ir. Baily counted the ribs, &c., in 

 no less than 117 specimens ; and it would appear that the number in different specimens, 

 old and young, varied from ten to sixty, but that the transverse fringes did not 

 augment in number in a similar ratio to the number of ribs. 



To one of the varieties with fewer and larger ribs the designation of Aspera has been 

 applied; but both Hisinger, in 1831, and Lindstrom, in 1S60, agree in considering this 

 last as a variety of ^. reticularis, differing only in shape ; Lindstrom obsening, at the same 

 time, that the Linnean form varies, like all those species which possess an extended horizontal 

 and vertical distribution (E. Forbes). In Gothland he finds coarse-ribbed specimens of 

 A. reticularis similar to those that occur in the Devonian formation ; but these variations 

 are connected with the fiuely ribbed varieties by every possible gradation and intermediate 

 shape; and the same occiurs in Great Britain.^ In Plate XIV I have endeavoured to 

 represent some of the principal shapes assumed by this shell, and have given illustrations 

 of the interior of both valves, as well as of its internal casts ; and in Plates X and XI of 

 my ' Devonian Monograph' will be foimd additional figures, completing the external and 

 internal details we now possess in connection with this species. M. Barrande, in his 

 valuable 'Monograph of the SUurian Brachiopoda of Bohemia,' p. 95, describes two varie- 

 ties of A. reticularis as var. Verneuiliana and var. Murchisoniana (op. cit., PL XIX, 

 figs. S, 9). Both these modifications in shape occur in our Silurian rocks. Fig. 4 of oiu 

 plate is the var. Murchisoniana ; while figs. 6 and 7 represent the var. Verneuiliana. 



Position and Locality. Atrypa reticularis ranges from the Lower Llandovery to the 

 Upper Devonian ; the greatest range known of any Palaeozoic shell. It occm:^ in so 

 many places, that several pages could be filled, were it necessary to enumerate all those 

 with which we are acquainted. It is particularly abundant in the Llandovery and 

 Wenlock rocks. In England it is plentiful in the Wenlock Limestone and Shales at 

 Dudley, Wenlock Edge, and "VValsaU, in various locahties in the Malvern, Woolhope, 

 May Hill, Usk, Llandeilo, and Marloes districts, which will be found recorded at p. 27S 

 of Phillips and Salter's memoir, in the second volume of the ' Memoirs of the Geological 

 Siu-vey of Great Britain.' It is not uncommon in the Upper and Lower Ludlow rocks ; 

 and abounds, of large size, in the Aymestr\' Limestone. Thus, it occurs at Ridge Hill, 

 Walgrove Hill, Martley Road, CoUin's Green, in the Abberley district. At Backbury 



1 In describing this species at p. 198 of his 'British Pal. Fossils,' Prof. M 'Coy states : "It yaries 

 firstly, in the convexity of the valves, both as to degree, distance from the beak (at which it is greatest), 

 and equality ; some small varieties, and the young at all times, having the valves almost equally and 

 evenly convex ; secondly, in form, some, particularly the young and the small varieties, beiug nearly 

 orbicular ; others being elongate, and nearly triangular, from the width of the hinge-line and narrowness 

 of the front ; thirdly, in the number, thickness, and closeness of the ridges, and the scales which cross 

 them, both of which are often smaller and closer than in the typical variety." 



