F. Chapman: Victorian Fossils, Ft. VI. 17 



ostiolate form (with non-plicate median fold and sinus), since the 

 median fold, in the larger and fully-developed specimens, carries 

 a longitudinal gi'oove. 



Points of difference between the European S. laevicosta. Val. 

 and the Victorian S. yassensis, de Kon^: — 



The specimen which McCoy selected for figuring in the De- 

 cades is unusually large,'^ and at a. first glance, one acquainted 

 with the European species might see a general resemblance 

 between the two forms. 



The Victorian spirifer, however, is sub-ovate in outline, as in 

 the New South Wales specimens, rather than sub-quadrate, as in 

 the European form. The shell is less turgid, the compression also 

 affecting the median fold, which is not so inflated as that of S. 

 laevicosta; there is also a longitudinal groove usually present, 

 especially in the larger Victorian specimens, which is not seen in 

 S. laevicosta. This larger character reminds one of a similar 

 feature in the Devonian S. bifidus, Roemer^ and the Silurian S. 

 bijugosus, McCoy.*, The median sinus is narrower and deeper 

 in the central area, and not so acutely V-shaped on the posterior 

 margin of the shell. The shoulders on either side of the beak are 

 steeper and more concave. 



The plications are of the same average number in both cases, 

 and show a viiriation between 11 and 14 counted on either side 

 of the median fold. 



The width of the Victorian S. yassensis ranges from 13 to 

 50 nun. 



Spirifer yassensis was first named in MS. by the^ Rev. W. B. 

 Clarke;^ and it was afterwards described under the same name 

 by de Konick*^ from specimens obtained from the Devonian 

 limestones of Yass. As I have previously remarked, the New 



1 In this I have had the advantage of comparing a long series of the European S. laevi- 

 costa from the Eifel, in the Nat. Mus. Collection. 



2 Mr. A. J. Shearsb}', of Yass, informs me that he has met with equally large specimen, 

 in the Devonian of Yass, although the fossil is commonly like that figured by de Konick, 

 as regards size. There is also a larger specimen than that figured by McCoy in the collec- 

 tion of the National Museum, from Buchan, presented by C. W. Nicholson (See pi. v., 

 fig. 2, of this paper). 



3 Versteinerungen des Harzgebirges, 1843, p. 13, pi. iv., fig. 16. 



4 Synopsis Sil. Foss. Ireland, 1846, p. 36, pi. iii. fig. 23. 



5 Sedimentary Formations of New South Wales, 1875, 3rd. ed., p. 15. 



6 Foss. Pal. Nouv-Galles du Sud, 1876, p. 104, pi. iii., fig. 6. 



