219 



and in the number of the radial ribs. These differences are constantly 

 existent, and when taken in connection with the difference of their geological 

 age, led Di^ Koninck to regard them as independent species. 



However, the pictures of the two species now under consideration given 

 in the work of De Koninck on the Belgian Carboniferous Brachiopods, do not 

 present the diverse features that one would e.xpect from the verbal explana- 

 tion in the text. Neither in point of size nor in the form and the number of 

 the ribs, can the two be separated as fundamentally distinct from each other. 

 There are transitional stages in both of the two forms, some of which are 

 very closely aUied in spite of being drawn as different species. This fact will 

 be readily appreciated if one examines the pictures somewhat more carefully. 

 Upon the geological age of the two forms De Koninck seems to have laid 

 .somewhat too much stress. According to Trautschold this species was 

 found at Mjatschkowa in association with Spinfcr mosqiiotsis and other 

 upper Carboniferous fossils. The Russian material seems to be quite well 

 determined or identified, and consequently, Tr.\utschold may be relied upon 

 as a reporter of the upper Carboniferous RJiynchonclla pleiirodon. The 

 species may thus be regarded as existent up to the lower part of the upper 

 Carboniferous. Therefore the difference in the horizons in the lower Carboni- 

 ferous must be overestimated as specific difference. Fundamentally speaking 

 tiie difference of geological liorizons must not be taken as the basis (^f specific 

 distinction, but the opposite course may be followed. 



The Australian examples described as of the species just under considera- 

 tion by De Koninck are not very well characterized. The configuration of 

 the specimen is widely different from those drawn in his previous work. If 

 this can be called Rhyuclionclla plcnrodoii, then the specimens of liis 

 Rhyiichoiirlla Iwta no doubt represent individual variations of Rhynchonclla 

 pleurodoii. The writer is unwilling to accept unreserved!}' the Australian 

 form as Rliyiichoiiflla plcnrodoii. 



Of a large number of the figures of the species drawn by previous authors, 

 the ones most resembling the present specimens from China are those of fig. 

 2, pi. XXIII., of Davidson's monograph and figs. 3, 7, S, 9, 41, 42, and 43, 

 pi. 15 of De Koninck's Faune du Calcaire Carbonifere. Mere comparison of 



