SPIRIFERA. 63 



Reticdlaeia reticulata, M'Coy. Synopsis of the Carb. Limestone Fossils of Ireland, 



pi. xix, fig. 15, 1844, 



IMBBICATA, M'Coy. liud., p. 143. 



— LINEATA, M'Coy. Ibid. 



Maktinia stringocephaloides, M'Coy. f. Ibid., p. 141, pi. xxii, fig. 8. 

 Spirifera elliptica, M'Coy. British Palaeozoic Eossils, p. 427, 1855. 



— imbricata, M'Coy. Ibid., p. 429. 



LINEATA, M'Coy. Ibid. 



Of this species two principal varieties may be distinguished. 



1st. Var. a, LINEATA, Martin = imbricata, Sow. = Martini, Fleming = reticulata, 

 M'Coy. PL XIII, figs. 1—13. 



Spec. Char. Transversely oval, or sub-orbicular ; hinge line much shorter than the 

 width of the shell, cardinal angles rounded ; beaks more or less approximate and con- 

 siderably incurved. Ventral valve gently and evenly convex, rarely exhibiting any mesial 

 elevation. Dorsal valve rather deeper than the opposite one, uniformly convex or 

 presenting a shallow longitudinal depression, apparent only in the proximity of the front, 

 or extending to the extremity of the beak. Area small, with lateral margins obscurely 

 defined, fissure triangular, partially covered by a pseudo-deltidium. Surface of both valves 

 marked by numerous- and regularly imbricated lines, the radiating striaa being, either so 

 close that they can hardly be distinguished or varying in their degree of proximity, but 

 rarely in any place more than a line apart. The concentric lines differ likewise in a 

 similar manner, but are in general more widely separated, in some examples being barely 

 distinguishable, while at other times they form strong, broad, flattened, or slightly rounded 

 ridges. The spiral appendages occupy the greater part of the interior, and do not 

 difl;er in detail from those of other species composing, the genus. Two examples have 

 measured — 



Length 12, width 16, (Martinis type.) 

 „ 20, „ 23, depth 13 lines. 



2d. Var. j3, elliptica, Phillips. Figs. 1 — 3. 



Transversely elliptical, always wider than long, with an obtuse, slightly elevated mesial 

 fold in the dorsal, and a defined longitudinal sinus in the ventral one ; hinge Ihie rather 

 exceeding half the width of the shell ; area triangular ; fissure large, and partially closed 

 by a pseudo-deltidium ; beak rather small and incurved, but not contiguous to that of the 

 opposite valve. Surface ornamented by small radiating striae intersected by numerous 

 small concentric ridges. A large specimen has measured — 



Length 25, width 36, depth 18 hues. 



Obs. A difference in opinion has been expressed as to the specific claims of the shells 

 here combined under the single denomination of Sp. lineata, Martin ; and I am aware that 



