ATHYRIS. 



21 



Athyris pectinifera, J. de C. Sowerby. Plate I, figs. 50 — 56 ; Plate II, figs. 1 — 5. 



Atrypa pectinifera, J. de C. Sowerby. Min. Con., vol. vii, p. 14, pi. 616, 1840. 

 Cleiothyris pectinifera, King. Monograph of British Permian Fossils, p. 138, 



pi. x, figs. 1—10, 1850. 

 Spirigera pectinifera, Howse. Annals of Nat. Hist., vol. xix, 2d series, p. 51. 

 Athyris pectinifera, Dav. Bulletin de la Soc. Linneenne de Normandie, vol. ii, p. 14, 



pi. i, figs. 1—7. 



This shell assumes in general a more or less rounded shape, is transversely oval, rather 

 wider than long, and in dimensions (with its fringe) rarely attaining 12 lines in length by 

 14 in breadth. The valves are almost equally deep and convex ; the beak of the ventral 

 valve is short, incurved, and perforated at its extremity by a small circular foramen. The 

 external surface is regularly covered by numerous concentric scaly ridges of growth, from 

 each of which radiate closely set fringes of elongated, somewhat flattened, spines (PI. I, 

 figs. 50, 52, 54 ; PI. II, fig. 2). In the interior, the hinge is strongly articulated, the 

 dental or rostral plates offering by their position much solidity to the beak of the ventral 

 valve ; between these we find located the extremity of the beak of the smaller valve, as 

 well as the cardinal or hinge-plate, which is not very largely developed in the present 

 species. This hinge-plate is likewise perforated close to its summit (under the umbone) 

 by a minute circular aperture, 1 destined in all probability for the passage of the intestine ? 

 as we know that this organ occupies a place about similar in other genera {Bhynclionella, 

 &c.) of which the animal has already been studied. 

 On each side of this small hinge-plate and of its aperture, 

 exists a prolonged testaceous plate, situated at a higher 

 level, and forming the ledge or rim of the inner socket- 

 walls. These two prolongations become lengthened, and 

 give birth (while serving as points of attachment) to the 

 two lamellae {a), which, by their convolutions on either 

 side, constitute the spires, as well as the intermediate 

 process by which they are united. These spiral lamellae, 

 disposed vertically to the plane of the valve, converge at 

 first, then bending suddenly upon themselves, at a short 

 distance from their origin, outwards and backwards {b), 

 in the shape of a half circle, which, passing first close to 

 the sockets (5), then follows in the direction of the bottom of the valve (o, c), to become 



1 The hinge, the rostral plates, and the position of the minute circular aperture in the cardinal or 

 hinge-plate, have been described and figured by Professor King in pi. x, figs. 7 and 9, of his ' Monograph 

 of British Permian Fossils.' 



