BRACHIOPODA. 
235 
P. Nysius, P. tenuicosta* * * § P. Knappi, Hall and Whitfield, 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 
Gtjpidula 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. 
Bashkiricm, de Verneuil, and P. pseudobashkiricus, Tschernyschew. The shell 
described by Barrande. from the etage G 3 , 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 i-eg-ard to the significance of the terms P. Nysius and its varieties 
crassicosta and tenuicosta, from the Niagara rocks at Louisville. The species was desci-ibed as having from 
twenty-five to forty plications; to the coarsely plicate shells the former term was applied, and to the more 
finely plicate the latter. Between these shells there is evidently something more than difference in degree 
of plication. The finely plicate shells {tenuicosta) are smaller and have shallower valves and low, incon¬ 
spicuous beaks. Nettblkoth has shown that the character of the ornamentation of the smaller shells is 
persistent, not gradational. But the sexiaration fi-om P. Nysius of these two varieties leaves nothing to 
rej)resent the specific type. Therefore, instead of leaving the identity of P. Nysius to be merged between 
the two varieties, it will be better, and in accordance with rule, to assume the shell known a.s var. crassi¬ 
costa, the first of the varieties named, as the typical form of P. Nysius. For the other variety the name 
Conchidium tenuicosta will be used in ju-eference to Nettelroth’s xiTO^iosed term P. complanatus (lib. cit., 
p. 53). 
t Canadian Record of Science, p. 295. 1891. 
I It may be well to verify the geological horizon of this s^iecies before basing any conclusions upon its 
occurrence in the Corniferous limestone. 
§ Zeitschr. der deutsch. geol. Gesellsch., vol. xl, j). 588. 1888. 
