152 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxx. 



front of the center of the valve and generally its base extends farther 

 up toward the dorsal edge and not infrequentl}" reaches it. 



Strictly speaking, these bituberciilated species are not congeneric 

 with the original Silurian types of Beyrichia. The latter have three 

 nodes or lobes — a central one, usually the smallest and corresponding 

 to the posterior (smaller) node in these Carboniferous species, a larger 

 anterior lobe, and a posterior one that, like the anterior lobe, is gen- 

 erally developed into an incurving ridge. This posterior node is not 

 developed in the bituberculated group of species in question, and as 

 this group contains many species and represents a well-marked stage 

 in the development of the Beyrichiidte, a distinct generic arrange- 

 ment seems advisable. However, on account of the present uncer- 

 tainty respecting the limits of such related and not well-established gen- 

 era as Beyrichiopsls^ BcyrlchlcUcu and S[inaphe^ and, more especially, 

 because it may become desirable to modify the definition of the simi- 

 larly bituberculated genus UlrlcJiia so that it shall include them, it is 

 deemed advisable to defer proposing a new genus until comparisons 

 now in progress may be completed. It may be well to mention also 

 that the writers have in manuscript descriptiotis of two late Silurian 

 species from Maryland, having unquestionable athnities to Beyrlchia^ 

 in which the lobation of the valves is reduced to two small, ill-defined, 

 subcentral swellings situated on either side of a well-devoloped primi- 

 tian sulcus. 



Though variable in what are usually to be regarded as important 

 respects, the next following species, which belongs to the larger, 

 inequivalved group, still seems to conform in essential particulars 

 to the British species upon which Jones and Kirkb}'^ founded not 

 only one but three genera, namely, BeyrlcJilojjsis^^* Beyriehella'J^ (did 

 Sy/u(jjhe/ Besides, a number of species that can scarcely be distin- 

 guished generically from either Beyrichiella or Synaphc are described 

 by the same authors as true Beyrichije. Careful comparisons show 

 that the permanent as well as the variable featuivs of the lobation of 

 the valves is so nearly the same in all these ine((uivalved forms that 

 the present writers are inclined to doubt the necessity of more tiian 

 two, instead of four, distinct genera. Indeed, if the whole asseml)lage 

 were referred to a single comprehensive genus, with perhaps two or 

 three subgenera, the arrangement would have advantages over the 

 present classification. If the latter suggestion were adopted, Beyri- 

 chiella would be the main genus, Synaphe would drop out as a syno- 

 nym, and Beyrlehlopsix would ])e th(» su])generic designation for the 

 fringed species. A second subgeiuis. if found desirable, might then 

 be erected for the group of species of which Bcyrichni f(><ll<-(it<i ,]o\\i^>^ 



«Geol. Mag., 3d Dec, III, 1886, p. 434. 

 b Idem, p. 438. 



'•Carlwniferous Ostracoda from Ireland, Sci. Trans. Roy. Dublin Soo. (2), VI, 1896, 

 p. UtO. 



