﻿ATRYPA. 



59 



Obs. I am very uncertain whether Atrypa desquamata be really more than a variety 

 of A. reticularis, but since Sowerby, Phillips, M'Coy, Salter, and several other palaeonto- 

 logists have considered it different, I have described it under a separate head. The 

 chief difference consists in the beak of the shell under description possessing a well- 

 marked area and exposed foramina] aperture, this last being usually concealed in A. reti- 

 cularis from the great incurvation of the beak ; it is also usually less ventricose than the 

 Linnasan shell, and the concentric lines of growth or lamina? are obscurely marked on the 

 greater number of specimens I have been able to examine ; but this may be due to 

 fossilization. Prof. Phillips states that "the analogy of this beautiful fossil to Atrypa 

 prisca {reticularis) is considerable, but that the species are totally distinct." Prof. M'Coy 

 observes likewise, that " by cautiously breaking a specimen in the right direction he had the 

 pleasure of ascertaining the existence of the spiral appendages in this beautiful fossil, and to 

 demontrate their spiral convolutions in the plane of the lateral margins, instead of at right 

 angles thereto, as in different groups of Spirifera ; that they are of rather small size, the 

 diameter of the spires not exceeding half the width of the shell, so that they are not placed 

 one behind the other, but each occupies its own side of the median line. The pallial vessels 

 are large, composed of three or four main trunks on each side, branching once or twice to 

 the margin." 



Atrypa desquamata occurs abundantly in the Middle Devonian of Woolborough Quarry 

 Ogwell, Chircombe Bridge, &c. ; at Barton, Lummaton, and Hope's Nose, near Torquay ; 

 in the Plymouth limestone, at Datington, near Totness, and in several other Devonshire 

 localities. 



Atrypa flabellata, Gold/. MS. PI. XI, figs. 11, 12. 



Terebratula prisca, var. flabellata, Roemer. Rlieinisch. Uebergangsgeb. p. 6G, pi. 



v, fig, 4, 1844. 



— insquamosa, var. flabellata (partim), Schnur. in Dunker und von 



Meyer's Palseontographica, p. 

 182, pl.xxiv, fig. 5, c d e, 1852. 



Spec. Char. Shell ovate, sometimes circular; dorsal valve uniformly convex, deeper 

 than the opposite one, at times ventricose. Ventral valve moderately convex; beak 

 incurved, with a circular foramen placed under its angular extremity, and almost entirely 

 surrounded by a deltidium, a flattened space or area existing between the beak-ridges and 

 hinge-line. Surface of each valve ornamented with from eighteen to twenty-four rounded 

 ribs, of which very few are due to bifurcation or interpolation. The surface is also marked 

 by a small number of concentric lines of growth. 



Length 13, width 11, depth 7 lines. 



Obs. Atrypa flabellata of Goldfuss has been considered by Bronn and F. Roemer to 



