Mr. T. R. Jones on Scandinavian Beyrichiae. 91 



gins, slight sulcus, and trace of central " lucid spot •" in which 

 characters we have a near approach to Leperditia. 



B. mundula differs from B. simplex, Jones (Quart. Journ. Geol. 

 Soc. vol. ix. p. 161. pi. 7. fig. 7), chiefly in its having a propor- 

 tionally longer hinge-line, or dorsal border, and a narrower pos- 

 terior extremity, and in frequently presenting a depressed Leper- 

 ditia-like aspect of the valves, which we do not find in B, simplex. 



The specimen here figured (fig. 23) is from the No. 1. lime- 

 stone, and is very convex and broadly oval in shape. The dorsal 

 border is, however, usually straight, two-thirds the length of the 

 valves, and from each of its extremities the margin has an oblique 

 direction downwards and outwards to about half the width of 

 the valve, where it meets the semicircular ventral border, and so 

 forms the more or less angular anterior and posterior extre- 

 mities of the valve, the former of which is somewhat narrower 

 and sharper than the latter. This outline, or an approximation 

 to it, is traceable in very many of the Beyrichice, but it is best 

 developed in the specimens of B, mundula above referred to, 

 from No. 5. limestone, in which the obliquity of the antero- 

 dorsal and the postero- dorsal angles of the carapace is as well 

 marked as in Leperditia, and is combined with a general de- 

 pression of the carapace-valves and other characteristics above- 

 noticed, which indicate a close relationship to the last-named 

 genus : — to this point we shall again refer in further descriptions 

 of the species of these genera. 



Of the three groups of the genus, that of the JugosiB is well 

 represented in the Scandinavian limestones under examination. 

 To this group also belong — 



Beyrichia Kloedeni, M'Coy. 



complicata, Salter. 



symmetrica. Hall. 



lata, Vanuxem, sp. 



Busacensis, Jones. 



Bohemica, Barrande, MS. 



The Corrugatce have here only two representatives {B. Wilck- 

 ensiana and B. siliqua). Possibly HalPs Cytherina spinosa may 

 be a Beyrichia of this type. An undcscribed species from Busaco 

 belongs to this group, and, taken together with B, Bohemica, 

 affords a passage into B. complicata of the Jugosce group. 



The little B. mundula above described has many larger con- 

 geners among the Simplices, such as — 



Beyrichia simplex, Jones, 



Logani, Jones, MS. 



strangulata, Salter, 



and several Bohemian forms collected by M. Barrande. 



