no. 1646. REVISION OF BEYRICHIIDM—TJLRICB AND BA.SSLER. 303 



The relations of the genus to the group of Beyrichia salteriana, 

 which section of Beyrichia includes the species most like h'la'denia, 

 have been discussed on a preceding page. 



Kloedenia may have been evolved through several rather widely 

 different ways. First, it may have been derived from the salteriana 

 group of Beyrichia by the ventral coalescence of the three lobes. 

 Though possible, even reasonable, the known species afford no satis- 

 factory evidence of such an alliance. In the absence of intermedi- 

 ate stages, the evidence must be admitted as wholly negative, if not 

 positively opposed to this view. Considering that the salteriana 

 group of Beyrichia is Silurian, and that Kloedenia-like ostracoda 

 began already in middle Ordovician time, it is clear that only a 

 part of the genus could have been descended from Beyrichia. 



According to the second view, Kloedenia was derived from some 

 unisulcate Primitian stock by the segregation and enlargement of the 

 post-median node. Suggestive resemblances may be noted on com- 

 parison with the Ordovician Primitia fytmidula, P. cincinnatiensis, 

 Eurychilina reticulata, and E.f subcequata. Regarding the two 

 valves of P. tumidula figured by Ulrich " as right valves, and com- 

 paring them with the right valve of Kloedenia initialis {Beyrichia 

 initialis Ulrich) figured on the same plate, the possible derivation 

 from Primitia is clearly indicated by correlation of the nodes and 

 furrows. It should be borne in mind, however, that this comparison 

 merely indicates the kind of steps by which passage from Primitia to 

 Kloedenia may have been effected, and not the links themselves, be- 

 cause K. initialis is older than either of the two Primitias mentioned. 



Still other derivations are suggested by the new Ordovician species, 

 K. pramuntia. This is a larger shell than any Primitia and has the 

 median lobe too well separated to recall that genus. Except for the 

 much sharper definition of the Kloedenia characteristics, this species 

 resembles leperditellsB like L. germana and A./ dorsicornis. But it 

 recalls even more Drepanella elongata, which differs in little that 

 may be called essential except that it has the sickle-shaped ridge of 

 Drepanella. This ridge is weaker in I>. elongata than usual, and it 

 is really conceivable that it might have become obsolete early in the 

 descendants of this species, and thus give origin to a stage that, with 

 our present limited knowledge, must be referred to Kloedenia. 



These diverse, yet all reasonably possible, derivations of Kloedenia 

 illustrate the extreme difficulties encountered in determining the 

 genetic relations of the major groups of the family Beyrichiidse. 

 Though inclined to favor the view that the majority of the species 

 referred to Kloedenia were evolved out of Primitia, it must be admit- 

 ted that the evidence is far from conclusive. 



«Geol. and Nat. Hist. Surv. Minnesota, Final Kept, III, Pt. 2, ls;>4, pi. 

 xliii, figs. 62-65. 



