191 
Relations and Differences. — This species differs from S. convolutus, 
J. Phillips, by the simplicity of its ventral furrow, and of its lateral folds, 
also by the form of its internal cast, which by the slight development of its 
muscular impressions resembles S. mosquensis, Pischer, much more than 
S. convolutus, J. Phillips. It cannot he confounded with my S. Roemerianus, 
on account of its size, the length of its area, and the absence of imbricated, 
plates which cover the surface of this last. 
Horizon and, Localities. — This Spirifer has been found in the hard 
shales of Le win’s Brook by Mr. McCoy ; and in those of Colocolo by the Bey. 
Mb B. Clarke. 
Spirifer triangularis, TF. Martin. 
PL XIY, Fig. 4. 
Conchy Uolithus anomites triangularis, W. Martin, 1809, Petrif. Derbiensis, p. 10, pi. 
36, fig. 2. 
Spirifer triangularis, J. Sowerby, 1827, Min. Concb., VI, p. 120, pi. 62, fig. 5, 6. 
,, ,, Fleming, 1828, Brit. Animals, p. 374. 
,, triangularis ? J. Pliillips, 1836, G-eol. Yorkshire, II, p. 217, pi. 9, fig. 12. 
,, ,, L. V. Buch, 1837, TJeber Deltliyris, p. 37. 
,, „ Idem, 1840, Mem. Soc. Geol. France, lY, p. 182, pi. 8, fig. 5. 
„ ,, L. G. de Koninck, 1843, Descr. Anim. Foss. Terr. Garb. Belg., 
p. 236, pi. 15, fig. 1. 
S'pirifera ornithoryncha, F. McCoy, 1844, Synop. Garb. Foss. Ireland, p. 133, pi. 21, fig. 2. 
Spirifer triangularis, P. v. Semenow, 1854, Ueber Foss. Schles. Kohlenkalkes, p. 30. 
Spirifera ornithoryncha, McCoy, 1855, Brit. Pal. Foss., p. 418, pi. 3d, fig. 27. 
,, triangularis, T. Dayidsou, 1859, Mon. Brit. Garb. Brack., pp. 27 and 223, pi. 
5, fig. 16-24 and pi. 50, fig. 10-17. 
This shell varies greatly in its shape ; generally it is much broader 
than long, while very occasionally its length equals its breadth. The only 
specimen sent me from Australia happens to be an example of this last, and 
consists merely of a ventral valve. This valve is subtetragonal, with slightly- 
rounded angles. It is small ; its proportionately broad and deep ventral 
furrow shows, towards its base, the mesial fold which characterises the species, 
and which often projects beyond the frontal margin. The ventral furrow is 
