Vol. 70.] THKOUGKE THE ANDES OF PEET7 AND BOLIVIA. 33 



A more or less typical example is figured by A. d'Orbigny ! under 

 the name of Terebratula peruviana . The same species is again 

 figured by Salter, 2 who refers it to Athyris subtilita (Hall). 



The Bolivian shells, however, are of a much smaller size than 

 Hall's species, 3 and seem to agree more closely with Seminula 

 subquadrata Hall/ The latter species does not appear to differ 

 to any great extent from the British Seminula ambigua (Sow.), 

 of which Dr. Vaughan has shown me examples from the Scottish 

 Coal Measures that are quite indistinguishable from my specimens, 

 the strongly-marked growth-halts and pronounced nature of the 

 median fold showing in general an advance on more typical 

 Avonian forms. 



Productus coea D'Orb. 



Examples of this species are everywhere numerous in the cherty 

 limestones around Lake Titicaca ; and, as A. d'Orbigny obtained 

 his type -specimens from this district (Yarbichambi), a further 

 description is unnecessary. 



An early mutation is well known from the Lower Carboniferous 

 of Great Britain, where it has been used as a subzonal index (S.,) 

 of the Avonian succession. 3 



A more advanced type, however, is the Productus cora from the 

 Permo - Carboniferous cora horizon of the Urals, 6 which differs 

 from the British form in its larger size and the possession of well- 

 marked spines irregularly scattered over the surface of the shell. 

 This old-age feature, unknown or extremely rare in the Avonian 

 mutation, is also characteristic of the Bolivian shells, and furnishes 

 additional evidence for regarding the limestones in which they 

 occur as of Upper Carboniferous or Permo -Carboniferous age. 



D'Orbigny' s original figures ~ are very much idealized, his type- 

 specimen being again figured in its natural state by Chernyshev. 8 



Typical spinose examples of this species also occur, though rarely, 

 in the Upper Productus Limestone of the Salt Range. 9 



Productus aff. spinulosus J. Sow. 



This form, which occurs in association with Productus cora, agrees 

 closely with Sowerby's species in the regularly-convex ventral valve 

 without a sinus, ornamented with irregularly-arranged, rounded, erect 

 tubercles which bear long slender spines. 10 It is, however, slightly 



1 ' Voyage dans l'Amerique Meridionale : Paleontologie ' 1842, pp. 36-37 & 

 pi. ii, figs. 22-25. 



2 Q. J. G. S. vol. xvii (1861) pi. iv, figs. 4 a & 46. 



3 See figures, ' Nat. Hist. N. Y. Pal.' vol. viii, pt. 2 (1894) pi. xlvii, figs. 19-21. 

 -1 Ibid. figs. 7-9. 



5 A. Vaughan, ' Palasontological Sequence in the Carboniferous Limestone 

 of the Bristol Area ' Q. J. G. S. vol. lxi (1905) p. 291 & pi. xxv, figs. 4-4 b. 



6 F. Chernyshev, Mem. Com. Geol. Russie, vol. xvi, No. 2 (1902) pi. liv. 



7 ' Voyage dans l'Amerique Meridionale : Paleontologie ' 1842, pi. v, figs. 8-10 



8 Mem. Com. Geol. Eussie, vol. xvi, No. 2 (1902) p. 622, fig. 69. 

 '■> W. Waagen, Pal. Indica, ser. 13, vol. i (1887) pi. lxvi, fig. 3. 



10 See T. Davidson, Mem. Palaeont. Soc. ' British Fossil Brachiopoda ' vol. ii 

 (1858-63) pi. xxxiv, figs. 18-21. 



Q. J. G. S. No. 277. n 



