152 



THE CAMBRIAN. 



| BULL. 81 



where it is found in association with Olenellus thompsoni and 0. vermon- 

 tana. The latter was referred to the new genus Mesonacis in 1885. 1 



Mr. S. W. Ford began, about 1868, a study of the rocks and fossils 

 of the hills east of Troy, New York, from which vicinity the first fossils 

 of the Olenellus fauna, found in New York, were obtained. These 

 were described by Prof. Hall, in 1847, and referred by him to the Hud- 

 son River group. Entering into correspondence with Mr. E. Billings, 

 and comparing the fauna he found at Troy with that from below Que- 

 bec, referred by Mr. Billings to the Lower Potsdam, he concluded that 

 the strata containing the fauna at Troy should be referred to an equiv- 

 alent horizon. In his first paper 2 he mentions finding eighteen species, 

 eight of which are referred to described species and ten remained to be 

 described. Mr. Ford published a number of papers from 1871 to 1885, 3 

 in which he described the rocks, and fossils found in them, that occur 

 near Troy, and also a little south of Schodack landing, in Columbia 

 County, N. Y. The fossils described by him are : Protocyathus rarum, 

 Archwocyathus rensselwricum, Obolella nitida, Scenella retusa, Hyolithes 

 emmonsi, H. impar, Agnostus nobilis, Leperditia troyensis, Microdiscus 

 meeJci, M. speciosus, and Solenopleura nana. One of the most interest- 

 ing of Mr. Ford's studies is that on the embryonic development of 

 Olenellus asaphoides. From the data thus obtained he decided that 

 the Olenellus fauna followed the Paradoxides fauna in time. 4 



1 Paleozoic notes ; new genus of Cambrian trilobites Mesonacis. Am. Jour. Sci., 3d ser.,vol. 29, 1885, 

 pp. 328-330. 



''Ford, S. W.: Notes on the primordial rocks in the vicinity of Troy, New York. Am. Jour. Sci., 3d 

 scr., vol. 2, 1871, pp. 32-34. Canadadiaa Nat., new ser., vol. 6, 1872, pp. 209-212. 



3 Descriptions of some new species of primordial fossils. Am. Jour. Sci., 3d ser., vol. 3, 1872, pp. 419- 

 422. 



On some new species of fossils from the Primordial or Potsdam group of Kensselaer County, New 

 York. Am. Jour. Sci., 3d ser., vol. 5, 1873, pp. 211-215. 



Remarks on the distribution of the fossils in the Lower Potsdam rocks at Troy, New York, with de- 

 scriptions of a few new species. Am. Jour. Sci., 3d ser., vol. 6, 1873, pp. 134-140. 



Note on the discovery of a new locality of primordial fossils in Rensselaer County, New York. 

 Am. Jour. Sci., 3d ser., vol. 9, 1875, pp. 204-206. 



On additional species of fossils from the primordial of Troy and Lansingburg, Rensselaer County, 

 New York. Am. Jour. Sci., 3d ser., vol. 11, 1876, pp. 369-371. 



Note on Microdiscus speciosus. Am. Jour. Sci., 3d ser., vol. 13, 1877, pp. 141, 142. 



On some embryonic forms of trilobites from the primordial rocks at Troy, New York. Am. Jour. 

 Sci., 3d ser., vol. 13, 1877, pp. 265-273. 



Two new species of primordial fossils. Am. Jour. Sci., 3d ser., vol. 15, 1878, pp. 124-127. 



Note on Lingnlella ccelata. Am. Jour. Sci., 3d ser., voL 15, 1878, pp. 127-129. 



Note on the development of Olenellus asaphoides. Am. Jour. Sci., 3d ser., vol. 15, 1878, pp. 129, 130. 



On certain forms of Brachiopoda occurring in the Swedish primordial. Am. Jour. Sci., 3d ser., vol. 15, 

 1878, pp. 364-366. 



Note on the trilobite Atops trilineatus of Emmons. Am. Jour. Sci., 3d ser., vol. 19, 1880, pp. 152, 153. 



Remarks on the genus Obolella. Am. Jour. Sci., 3d ser., vol. 21, 1881, pp. 131-134. 



On additional embryonic forms of trilobites from the primordial rocks of Troy, New York. Am. 

 Jour. Sci., 3d ser., vol. 22, 1881, pp. 250-259. 



Note on the discovery of primordial fossils in the town of Stuy vesant, Columbia County, New York. 

 Am. Jour. Sci., 3d ser., vol. 28, 1884, pp. 35-37. 



4 Embryonic forms of trilobites from the primordial rocks of Troy, New York. Am. Jour. Sci., 3d 

 ser., voL 22, 1881, pp. 250-259. 



