OSTRACODA. 657 



Bejrlchia.] 



thick, in a ventral view resembling lipsj surface of valves gently convex within the 

 wide concave border, the central part of the upper half depressed around a narrow 

 pit; in front of the pit occasionally a slight rounded elevation. Surface beautifully 

 marked with small pits closely arranged in concentric lines, usually less curved than 

 the ventral outline of the valves. 



This is one of the prettiest of the numerous Ostracoda occurring in the Trenton 

 of Minnesota. It is also one of the most easily recognized, the thick, lip-like edges, 

 and the concentric surface markings being unusually distinctive. 



Formation and locality. — Near the top of the Galena shales, Goodhue county, Minnesota. 



Genus BEYRICHIA, McCoy. 



Beyriohia, McCOY, 1846. Synop. SO. Fossi Ireland, p. 57. 



Carapace small, equivalved, oblong or semiovate, with a straight dorsal and 

 convex ventral outline. Typically each valve has two sulci and three lobes, of which 

 the central one is the smallest; th&two larger lobes often coalesce ventrally. Surface 

 usually marked with pittings, reticulation, papillEe or other ornament. 



Type: Beyrichia kloedeni McCoy. 



This genus, after Leperditia, is the most important of all the generic groups of 

 Paleozoic Ostracoda. Many of the species also, those of the Upper Silurian rock* 

 especially, are compar^itively large, specimens over 3 mm. in length being not at all 

 uncommon. The individuals, moreover, are generally abundant, layers of rock in 

 many instances being crowded with, if indeed they are not largely made up of their 

 separated valves. 



In the restricted sense in which the genus is here defined, the oldest known 

 species is the Minnesota form about to be described.* It is from the middle third of 

 the Trenton shales (?Black River group). Of the Trenton proper, B. Bella Walcotf, 

 may belong to the genus, and I have a doubtful species from the Utica horizon at 

 Cincinnati, Ohio; but so far we know of no true Beyrichia from the Hudson River or 

 Cincinnati group, those referred to the genus from this formation belonging to 

 Ctenobolbina, Drepanella, Bollia, Tetradella, Ceratella and Primitia. In the Clinton, 

 however, B. lata Hall (Vanuxem)-j- is a good species, and from here on to the close 

 of the Carboniferous system the genus is more or less well represented in every 

 group of strata. 



* Prof. T. Rupert Jones hasflescribed BeyrieMa holli from the MinEevian flags of Great Britain (Geol. Mag., u. ser., Dec. 

 2, vol. 8, p. 343; 1881), but the affinities of the fossil seem to me as doubtful. 



+ Not BolMa lata Jones, 1890; Quart. Jour. Geol. Soc, vol. 46, p. 12, pi. 3, figs. 1, 2, 3. The specimens identified by Prof. 

 Jones with B. lata are widely different from the typical Clinton form of this species, which is a true Beyrichia, but I 

 cannot distinguish them from BoUia symmetrica Hall, sp. 



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