

rALCorr] PALEONTOLOGY UPPER MISSISSIPPI. 227 



Palseacuiyea irvingi, p. 173. 



V 



Straparollus (Ophileta) primordialis, Winchell, as Ophileta (Raphi 



stoma) primordialis, p. 173. 

 Theca primordialis, Hall, as Hyolithes primordialis, p. 175. 

 Bellerophon autiquatus, Whitf., p. 176. 

 Conocephalitescalymenoides, Whitf., p. 179. 

 Crepicephalns onustns, Whitf., p. 182. 



Conoceplialil.es gibbsi, Whitf., as Crepicephalns? gibbsi, p. 184. 

 DiUelocephalus granulosus, Oweu, as Ptychaspis granulosa, p. 185. 

 Ptychaspis granulosa, Hall, as P. striata, p. 186. 



niiuuta, Whitf., p. 186. 

 Dikeloceplialus niinnesotensis Owen, p. 187. 

 Agraulos (Bathyurus?) woosteri, Whitf., p. 189. 

 Arionellus (Agraulos) convexus, Whitf., as Arionellus convexus, 



Whitf., p. 190. 

 Ellipsocephalus curtus, Whitf., p. 191. 



In the preliminary remarks on the fauna he says: 



It is a matter of considerable interest that, in different localities of the Potsdam 

 formation, the forms of trilobites found are generally specifically distinct ; and not- 

 withstanding the large number of species already described from this formation, both 

 in this State and other parts of the country, other new forms, readily detected by 

 those familiar with the several details of structure peculiar to these animals, are met 

 with at almost every new locality examined. This change in species between dif- 

 ferent localities is usually accompanied also by some slight difference in the material 

 or composition of the rock, which not only shows that the species were of short dura- 

 tion in time, or that they were restricted to limited geographical areas, but that a 

 change in the conditions of life and circumstances under which the animals existed, 

 and with which they had to contend, was constantly taking place. How much these 

 circumstances or conditions had to do with the production of forms, or modification 

 of types among them, it would be difficult to determine; but one thing is certain, 

 that where the same character of rock and apparent conditions of deposition prevail 

 over a limited geographical area, or are repeated within a slight vertical range, we 

 are pretty sure to find the same, or closely allied forms represented, showing that 

 under like conditions similar forms prevail. 1 



In 1883, when describing the life of the Potsdam epoch, in the Gen- 

 eral Geology of Wisconsin, Prof. T. G. Ghamberlin illustrates the fol- 

 lowing species : 2 



Palreophycus plumosus, p. 125, Fig. 11. 

 Bellerophon antiquatus, Whitfield, p. 126, Fig. 12, a, b. 

 Ophileta primordialis, Winchell, p. 126, Fig. 12, c, d. 

 Holopea sweeti, Whitfield, p. 126, Fig. 12, e. 

 Palieacma3a irvingi, Whitfield, p. 126, Fig. 12, f. 

 Platyceras primordialis, Hall, p. 126, Fig. 12, g. 

 Serpulites murchisoni, Hall, p. 126, Fig. 12, h. 

 Theca primordialis, Hall, p. 126, Fig. 12. i. 

 Dendrograptus hallianus, Prout, p. 126, Fig. 12, j. 

 Lingula antiqua, Conrad, p. 127, Fig. 13, b. 

 Lingulella stoneana, Whitfield, p. 127, Fig. 13, a. 



aurora, Hall, p. 127, Fig. 13, c. 



ampla, Hall, p. 127, Fig. 13, d. 



mosia, Hall, p. 127, Fig. 13, e. 



•Op. cit., pp. 163. 164. 



•General Geology. Historical Geology. Paleozoic Era. Geol. Wis. Survey of 1873-1879, vol. 1, 1883. 



