Mr. T. R. Jones on Scandinavian Beyrichige. 87 



transverse furrow into two oval bosses of unequal size, the lower or 

 ventral one being the largest and often becoming in the adult a 

 protuberance of great (relative) size, and so prominent as to render 

 the anterior part of the valve broader than the posterior (figs. 7 

 & 8). The central ridge is usually reduced to an oval boss, 

 isolated and placed rather obliquely. The posterior or largest 

 ridge is well developed, strongly curved, thick above and taper- 

 ing downwards and forwards, until it terminates nearly opposite 

 and near to the lower end of the central boss, with which it 

 sometimes shows an inclination to unite at a sharp angle. At 

 its thickest part, the posterior ridge is divided obliquely and 

 transversely, by two, slight, narrow, sinuous furrows, into three 

 parts, which vary in their distinctness in nearly every individual : 

 sometimes a third similar furrow again divides this ridge in its 

 ventral portion (fig. 8). 



The surface of the valves is coarsely granulated, except in the 

 very young state. 



This species differs from B. Buchiana in its larger bulk, its 

 coarser aspect, its granulations, and especially in the disposition 

 of the surface-ridges. The same general arrangement of these 

 exists in both species, but in B. tuberculata they have a greater 

 development and are more subdivided; the horse-shoe ridge 

 especially of the one is broken up in the other species. 



This is evidently the species illustrated by Kloden^s figures 

 20-23; and it is therefore the typical Beyrichia tuberculata. 

 The other figures (16-19) referred by this author to the young 

 state of the same species, belong to our new species B. JVilcken- 

 siana, to be presently described. 



B. tuberculata, var. nuda. PI. V. figs 10, 11. 



A smaller-sized variety of this species occurs plentifully in 

 another block of limestone. The surface is destitute of tubercles ; 

 and the ventral anterior lobe does not appear to attain the ex- 

 cessive growth that is seen in old specimens of the typical form. 



B. tuberculata, var, antiquata. PI. V. fig. 12. 



A large and unique left carapace-valve, from No. 5 lime- 

 stone, exhibiting the usual arrangement of the surface-lobes of 

 this species, except that the posterior ridge is not quite so largely 

 developed, has a perfectly smooth surface, and a trenchant 

 margin well armed with spines on the front, hind, and lower 

 borders of the valve. This spiny or denticulated condition of 

 the margin I have not met with in other varieties of this species ; 

 but it occurs in two figures (20, 21) of M. Klodeu's typical 

 form. 



