Palceozoic Bivalved Entomostraca. 303 



Carboniferous and Permian strata ; it is now evident that 

 they had a very wide pjeographical range. 



The specimens chiefly belong to species of Bairdia. They 

 have evidently been obtained from a hard dark-coloured 

 limestone. Nearly all of them are complete carapaces, not 

 single valves. The ])articulars sent to us as to locality are 

 that they were found in tlie " Carboniferous Limestone of the 

 Kiver Bardun, falling into the River Ezsin, South Mon- 

 golia " ^. 



The following brief notes refer to the species and varieties 

 determined by us. 



1. Leperditia Okeni (Miinster), and var. inornata (M'Coy). 

 (PI. XVI. tigs. 1 and 2.) 



Leperditia Okeni, Jones and Kirkby, 1S65, Ann. & Mag. Nat. Hist, 

 ser. 3, vol. xv. p. 406, pi. xx. figs. 1-3 ; and var. inornata (M'Coy), 

 cp. cit. vol. xviii. 1866, p. 44. 



Several examples of tliis species and its varieties occur in 

 (his set of Ostracoda. Fig. 1 represents a good example of 

 the typical form. Fig. 2 is from a specimen that agrees 

 closely with the variety inornata (M'Coy). There are 

 other individuals belonging to a variety larger than either of 

 these, being fully one ninth of an inch long and more oval in 

 outline. These are similar to an unnamed form (hitherto 

 grouped with the species) from Holwell, in Somerset, and 

 other localities. 



Z, Okeni (with its varieties) is a common and widespread 

 species in the Carboniferous-Limestone series. In these rocks 

 it occurs in England, Scotland, and Ireland ; and it has been 

 found in strata more or less equivalent in Nova Scotia, 

 Belgium, Germany, Russia f, and now in Mongolia. 



2. Bythocypris hihhata (Miinster). (PL XVI. fig. 3.) 



Cythere hilobata, Miinster, Jones and Kirkby, Ann. & Mag. Nat. Hist, 

 ser. 3, vol. xv. 1865, p. 409, pi. xx. fig. 10. 



There are three examples of this species, all of which are 

 similar, both in size and in other respects, to British specimens. 



This species occurs in the Carboniferous Limestone of 

 Russia, Bohemia, Belgium, and England. 



• See also ' La Faune du Calcaire Carbonifere Inftrieur du BardouQ 

 en Mongolia,' par P. Venukoff : 8vo, St. Petersburg, 1888, in Rusdaa 

 and French, pp. 211 and 225. 



t See Ann. & Mag. Nat. Hist. ser. 4, vol. xv. 1875, p. 54. 



