6A 



short edge, and near the other there is a lobe, cut across by two 

 furrows into three parts. In the space left between these lobes and 

 the straio-ht edge, there is an oval node, the long axis of which 

 stands at right angles on the straight edge. This latter node is 

 situated nearest to that short edge close to which the two nodes are 

 found. Of these latter the one that is at the greatest distance from 

 the straio-ht edge, is sometimes considerably swollen. Such valves 

 are assumed to have originated from female individuals and the 

 swollen node to have served as ovarian pouch. 



That this Ostracod is so universally known is undoubtedly due 

 to its frequent occurrence in the upper silurian Beyrichian limestones 

 of which a great many erratic boulders of Lower Germany consist. 

 In our diluvium too such boulders are by no means rare. 



But however well-known this species of Ostracoda may be, it 

 soon appears on examining the literature on the silurian forms that 

 the orientation of the shells is still doubtful, in other words which 

 valves are to be considered as right ones and wdiich as left. 



Now the purpose of this paper is to solve this problem. 



Before proceeding to this, however, I will tirst give a short account 

 of the history of this problem. 



The first person wliom we may suppose to have been acquainted 

 with this Ostracod, is Leopold von Buch (3, p. 71;. In 1828 he gave 

 a representation of a piece of Beyrichian limestone and in this 

 described Chonetes striateUa Dalm. sp., which he called Leptaena 

 lata and to which he gave the shells of Tentaculites as spines. To 

 the Ostracoda found in this rock he gave the name of "Leptaeimi- 

 brut." It is quite possible that among these there were also valves 

 of Beijrichia tuhercidata, but this cannot be ascertained from the 

 pictures. Von Buch does not mention the orientation of the shells. 



Neither do Klöden (4, p. 112) and Burmeistek (5, p. 72), who 

 took the Ostracoda valves for cephalic and caudal shields of Tribo- 

 jites. Klöden was the first who in 1834 gave a clear representation 

 of Betjrichia tuhercidata as one of the forms which he classified 

 among Battus tiibermlatus. 



Not until 1845 does Beyrich (6, p. 47) assert that Battus tuber- 

 eulatus is no trilobite on account of the asymmetry of the remains, 

 but must be classified among the Ostracoda as it has a bivalved 

 carapace. Later, in 1846, M'Coy (7, p. 57) and independently of 

 him, Boll (8, p. 127) in 1847 instituted the genus Beyrichia. Only 

 the former gives a sufficient account of the criteria of the new genus. 



This author is the first in W'hose works we can find something 

 about the question we are going to solve. 



