A CARBONIFEROUS FAUNA FROM NOWAJA SEMLJA. 157 



Class BRACHIOPODA. 



Judging from the materials at hand, Brachiopods are highly characteristic of the 

 Cape Cherney limestone, where they probably exhibit a rich and varied character, to 

 which full justice cannot be done here, on account of the fact that many of the most 

 interesting forms observed came to grief when being developed, or were so sparsely 

 represented as to preclude the possibility of making satisfactory serial sections. 



Modern workers on fossil Brachiopods have shown that within certain groups there 

 can occur remarkable phenomena of homoeomorphy and convergence which often make 

 it impossible to estimate the true genetic affinities of many species, unless a knowledge 

 of their internal characters be obtained. Such instances of forms differing in the nature 

 of their internal characters, although apparently nearly allied so far as their general 

 appearance indicated, were met with in a few cases, especially among the Spiriferids, 

 and will be referred to in due course. 



The mode of .occurrence of the various species shows that peculiar conditions, not 

 yet understood, affected the development of some forms more than others. For 

 instance, it is difficult to explain how it is that Productus longispinus J. Sow., is 

 represented by full-grown individuals only, as is also Productus giganteus (Mart.), 

 whilst Productus elegans M'Coy, is represented by a series of specimens ranging in 

 length from a few millimetres to about 40 mm. The explanation may be that conditions 

 which killed the immature individuals of the latter, left those of the former unaffected ; 

 this explanation seems more satisfactory than that based on the assumption that the 

 nature of the shell in the young stages of Productus longispinus and Productus 

 giganteus was such as to render fossilisation impossible. 



The assemblage as a whole is quite normal, and there is no evidence of dwarfing or 

 of a depauperised condition. 



Terebratulid^e. 



Genus Dielasma King. 



Dielasma lenticulare de Koninck. (PL I. figs. 10-1 0c.) 

 Db Koninck, Faune du Calcaire Carbonifere, 6 roe partie, 1887, p. 17, pi. 2, figs. 1-9. 



Few of the numerous species of Dielasma established by de Koninck have been 

 unreservedly adopted in pal?eontological literature, but the well-defined characters of 

 his Dielasma lenticulare justify its claims to specific distinctiveness. The Dielasma I 

 refer to it is, like the Belgian form, lenticular and globose, with non-sinuate valves. 

 Frontally, the junction line is perfectly straight. It is represented by a complete 

 specimen, the dimensions of which are : length, 7 mm. ; breadth, 6 mm. ; depth, 5 mm. 

 A large pedicle-valve, measuring approximately 20 ram. in length, probably belongs to 

 the same species. Comparison with Davidson's figures will show that it cannot be 



