Mr. T. R. Jones on Scandinavian Beyrichia;. 85 



^hc several forms of the Beyrichits obtained from the lime- 

 stone fragments are illustrated in Plate V., and I now proceed 

 to their description (premising that the figures represent the 

 specimens magnified 4 diameters). 



Class CRUSTACEA. 



Subclass Entomostraca. 



Order Phyllopoda ? 



Family Limnadiad^ ? 



Genus Beyrichia, M'Coy, 1846 (Synop. Sil. Fos. Ireland, p.57). 



Generic characters. — Animal enclosed in a vertical bivalved 

 carapace. Carapace equivalved. Carapace-valves oblong ; anterior 

 (cephalic) and posterior (caudal) extremities somewhat rounded ; 

 inferior (ventral) border semicircular ; superior (dorsal) border 

 straight. Valves wider at the caudal than at the cephalic extre- 

 mity ; more or less convex ; impressed with one or more trans- 

 verse furrows, commencing on the dorsal or hinge border, and 

 variously modifying the surface of the valve. Hiugement not 

 known ; probably a simple adaptation of the thin dorsal edges 

 and their union by membrane. 



\st Gh'oup : SixMPLiCES. — Surface of valve simple, almost uni- 

 formly convex, but impressed with one, usually short, vertical, 

 dorsal furrow on the anterior half of the valve, and (if extended) 

 dividing the surface of the valve into two unequal parts (the 

 anterior portion being the smaller). Valves either with simple 

 edges, or bordered (except on the dorsal edge) by a narrow flat- 

 tened rim ; in the first case the margin of the one slightly over- 

 lapping that of the other valve, when united ; in the second case, 

 the opposite flat borders coming in contact, 



2nd Grou2i : CorrugaTjE. — Surface of valve convex, impressed 

 with two vertical furrows, not reaching across the valve, but 

 marking out three unequal lobes on the surface and giving it a 

 crumpled appearance. The anterior furrow holds the same rela- 

 tive position as the single furrow in the "Simplices." The 

 valves are bordered (on three sides) by a narrow depressed 

 margin. 



3rc? Group : Jugos^. — Surface of valve impressed with two 

 or three strong vertical furrows, extending from the back to the 

 ventral portion of the valve, and dividing the surface into three 

 or more unsymmetrical lobes, transverse ridges, or bosses, which 

 vary considerably in their size, mode of subdivision, and relative 

 position in different sjjccies, and, to some extent, in different 

 stages of growth of individuals. The anterior, inferior, and pos- 



