ATHYRIS. 77 



Genus — Athyris, M'Coy, = Spirigera, B'Orbigny. 



See article Athyris, ' Monograph of British Permian Brachiopoda/ Part IV, pp. 20 — 

 22, 1857. 



Athyris ambigua, Soiverby. PI. XV, figs, 16 — 22. 



Spirifer ambiguus, Sowerby. Min. Con., vol. iv, p. 105, tab. ccclxxvi, Nov., 1822 {Atrypa 



of the index). 

 Terebratula ambigua, Phillips. Geol. of York., p. 221, pi. xi, fig. 21, 1836. 

 ? — pentaedra, Phillips. Ibid., pi. xii, fig. 3. 



Atrypa sublobata, Portlock. Report on the Geology of the Coast of Londonderry, &c., 



p. 567, pi. xxxviii, fig. 2, 1843. 

 Terebratula ambigua. Be Koninck. Animaux Fossiles de la Belgique, p. 296, pi. xx, 



fig. 2, 1843. 

 — — M.V. K. Geo], of Russia, vol. ii, pi. ix, fig. 12, 1845. 



Spirigera ambigua, D'Orbigny. Prodrome, vol. i, p. 151, 1849. 

 Athyris ambigua, M'Coy. British Palaeozoic Fossils, p. 432, 1855. 



Spec. Char. More or less obscurely pentagonal, rather wider than long, moderately 

 convex ; beak not much produced, incurved ; foramen small, circular, contiguous to the 

 umbone of the opposite valve ; a longitudinal, somewhat angular sinus extending from the 

 extremity of the beak to the frontal margin. Dorsal valve almost evenly convex, or obscurely 

 trilobed, the central lobe or fold being more often broad, and longitudinally divided by a 

 narrow mesial groove ; front deeply undulated. External surface smooth, marked only by a 

 few concentric lines of growth. Shell structure not perforated. In the interior the spiral 

 appendages are directed outwards, filling the larger portion of the shell. Dimensions very 

 variable ; three examples have measured — 

 Length 14, width 12, depth 8 Hues. 



» 10 „ 11 „ 7 „ 



j> lOg „ IO2 ,, 8 „ 

 Obs. This species varies considerably in the details of its external shape. It is some- 

 times nearly equally and evenly convex (especially in young shells), with hardly any definite 

 mesial elevation in the dorsal valve (figs. 21, 22, 23), while at other times the appearance 

 of the shell is obscurely trilobed, and when the fm-row along the middle of the fold is 

 stronglymarked it sometimes resembles certain examples of the Jurassic Terebratula quadri- 



Mr. J. H. Burrow, to whom I am greatly indebted for much valuable and liberal assistance, has informed 

 me that he has found the following Spirifers in the Lower Scar Limestone of Settle, in Yorkshire: 1. Sp. 

 striata; 2. S. duplicicostata ; 3. Sp. crassa ; 4. Sp. planata ; 5. Sp. fusiformis ; 6. Sp. triangularis; 

 7 . Sp.triyonalis ; 8. Sp . bisulcata ; 9. Sp. convoluta ; 10. Sp. grandicostata ; 11. Sp. cuspidata; 12. Sp. 

 triradialis ; 13. Sp. pinguis ; 14. Sp. ovalis ; 15. Sp. integricosta ; 16. Sp. glabra; 1/. Sp. lineata I 

 18. Sp. octoplicata ; 19. Sp, insculpta ; 20. Sp. Reedii and C. teptosa. 



