BRACHIOPODA. 235 



P. Nysius, P. ienuicosta* P. Knappi, Hall and Whitfiuld, and the shell described 

 in this work as Conchidium Greenii, sp. nov., from the Niagara dolomites of 

 south-eastern Wisconsin. There are some other American species of this 

 genus of more distinctly local and restricted groups, such as the so-called 

 Gypidula unguiformis, Ulrich, Pentamerus Colletti, Miller, P. decussatus, Whiteaves, 

 the last recently described from the yellow dolomites of the Grand Rapids of 

 the Saskatchewan River ;f all of which are concentrically striated and finely 

 plicated species. Another form, small and very coarsely ribbed, is the 

 C. crassiplica, sp. nov. 



Conchidium makes its appearance in America in the fauna of the Niagara 

 dolomites in the states of Wisconsin, Iowa, Illinois, Indiana and Kentucky, 

 while it is not known in the equivalent fauna of New York. In like manner 

 it appeared in the faunas of the Wenlock and Aymestry of England, and at an 

 equivalent horizon in Gotland, Esthonia and Bohemia. It does not occur in 

 the Lower Helderberg, nor in the earlier faunas of the Upper Helderberg ; its 

 latest representative in this country is Nettelroth's P. Knighti (== C. Nettelrothi, 

 nom. nov.), said to be from the Corniferous limestone.^ In Europe it is 

 continued to a later date in the large Russian middle Devonian species P. 

 Bashkiricus, de Verneuil, and P. pseudobashkiricus, Tschernyschew. The shell 

 described by Barrande from the etage G-, as a lamellibranch, under the name 

 Zdimir solus, has been shown by Novak to be a pentameroid of this plicate 

 type § 



* There remains some obscurity in regai-d to the significance of the terms P. Nysiiis and its vaiieties 

 cmssicosfa and ttmiiuosta, from the Ni.<ig:ara rocks at Louisville. The species was described as having from 

 twenty-five to forty plications; to the coarsely plicate shells the former tejm was applied, and lo the more 

 finely plicate the latter. Between these shells there is evidently something more than difVerence in degree 

 of plication. The finely jilicate shells [tenuicosta) are smaller and have shallower valves an<l low, incon- 

 spicuous beaks. Nkttelroth has shown that the character of the ornamentation of the smaller shells is 

 persistent, not gradational. But the separation from P. Nystius of these two varieties leaves nothing to 

 represent the specific type. Therefore, instead of leaving the identity of P. Nysiiu> to be merged between 

 the two varieties, it will be better, and in accordance with rule, to assume the shell known as var. crassi- 

 costa, the first of the varieties named, as the typical form of P. Nysiv^. For the other variety the name 

 ConcUdlum tenuicosta will be used in preference to Nettelroth's proposed term P. compUmatns (lib. cit., 

 p. 53). 



t Canadian Record of Science, p. 295. 1891. 



X It may be well to verify the geological horizon of this species before basing any conclusions upon its 

 occurrence in the Coi-niferous limestone. 



§ Zeitschr. der deutsch. geol. Gesellsch., vol. xl, p. 588. 1888. 



