86 Mr. T. R. Jones on Scandinavian Beyrichise, 



terior margins of each valve are turned sharply inw^ards, the 

 angle so made being marked externally by a prominent ledge, 

 either slightly rounded or trenchant (and sometimes spiny), 

 forming a narrow depressed border along these three edges of 

 the external surface of the valve. These edges of the valves 

 close together by the marginal flange of the one valve being re- 

 ceived within that of the other, — somewhat like the fitting of the 

 lid and body of a circular snuff-box. United valves are very 

 rare ; one such specimen shows the ventral margin of the left 

 valve overlapping that of the right. There is no marked differ- 

 ence in the shape of the two valves ; and the size of the valve 

 that is received within and overlapped by the other is very little 

 less than that of its fellow. 



(JUGOS^.) 



1. Beyrichia Buchiana, nov. sp. PI. V. figs. 1-3. 



Surface of valve impressed with three transverse furrows ; the 

 antei'ior and central ones reaching across the valve, and separated 

 by a narrow ridge ; the posterior furrow extending about two- 

 thirds of the width across, and bounded by a semicircular ridge. 

 In other words, the exterior of the valve presents three trans- 

 verse ridges ; the anterior is isolated, narrow, and slightly curved ; 

 the other two, occupying the posterior half of the valve, are 

 united towards the ventral border, and form a compressed semi- 

 circular or horse-shoe ridge, with its convexity downwards. The 

 posterior arm of this horse-shoe-shaped ridge is larger than the 

 other arm (or median ridge), and is sometimes indented by a 

 slight, short, oblique furrow on its outer ridge (fig. 2) ; and 

 sometimes it is tuberculated (fig. 3) . The anterior and posterior 

 margins of the valve are also roughened with spinose tubercles 

 in old specimens. 



This form presents a well-marked and simple pattern of the 

 surface, to which we can conveniently refer for comparison in 

 describing others. Only one of our limestone fragments affords 

 this s))ecies, and in this it occurs in great profusion, together 

 with B. IVilckensiana, Tentaculites, and Leptiena lata. 



A very similar limestone a])pears to have furnished the spe- 

 cimens figured in the ' Kccueil dcs Tetrif. Remarq.," and which 

 indeed are possibly referable to this species : — a coincidence 

 which has led me to dedicate this well-characterized Beyrichia to 

 the memory of M. von Buch. 



2, Beyrichia tuberculata, Kloden, sp. PI. V. figs. 4-9. 



Surface of valve embossed with three lobes or ridges. The 

 anterior ridge is usually divided more or less decidedly by a 



