THE ANNALS 



AND 



xMAGAZIXE OF NATURAL HISTORY. 



[SECOND SERIES.] 

 No. 92. AUGUST 1855. 



VI. — Notes on Palceozoic Bivalved Eatomostraca, No. 1. Some 

 Species of Bcyrichia fi'om the Upper Silurian Limestones of 

 Scandinavia. By T. Rupert Joxes, P.G.S. 



[With a Plate.] 



Amongst the small bivalved Entomostraca found in the Lower 

 Palseozoic rocks are several species of the genus Beyrichia, for 

 the elucidation of which we are chiefly indebted to MM. Kloden, 

 Beyrichj M'Coy, and Salter. The Beyrichia occur very low dowTi 

 in the geologic series, though they are not the first to indicate 

 the Crustacean class in the fossiliferous rocks. 



The carapace-valves of these little Crustaceans are usually ob- 

 long in shape, and rarely exceed j^th of an inch in length ; the 

 more typical forms have their surfaces embossed with two, three, 

 or more transverse ridges or isolated protuberances. Some spe- 

 cimens in theii' general contour and in the arrangement of the 

 inequalities on the surface of the valve offer a distant resemblance 

 to a miniature human ear. Other varieties have smooth valves, 

 more or less indented by a transverse furrow which divides the 

 surface into two unequal parts. 



The remains of Beyynchia are met with, both as calcareous 

 carapace-valves (by far most usually separate), and as casts of 

 single valves, scattered more or less abundantly in the substance 

 of the rock or on the planes of stratification. Not unfrequcntly 

 they have been distorted by the movements which the integral 

 parts of the rock have suffered in the process of partial meta- 

 moi-phism. The carapaces themselves, generally as single valves, 

 are frequently met with in the Upper Silurian rocks of Britain, 

 though not in the Lower Silurian ; and they abound in some of 

 the Upper Silurian rocks of Sweden. Yet our observations arc 

 often necessarily limited to the casts of the exteriors and the 



Ann. 6j- May. N. Hist. Ser. 2. Vol. xvi. 6 



