152 PROCEEDINGS OF THE NATIONAL MUSEUM. V0L.xxn. 



Age of Silliman's Fossil Mount. — From Mr. Porter's description, it 

 will be seen that the fossils recently collected at Silliman's Fossil 

 Mount are from various horizons, and yet there is nothing to indicate 

 the presence of more than one fauna. The foregoing list shows that at 

 present there are 72 species known from this locality, and of these 28 

 are restricted to it, There are, therefore, 54 species which are common 

 to other localities, a goodly number with which to make safe correla- 

 tions. Of these 54 species, 41, or 57 per cent of the known fauna, are 

 also found in the region of Minnesota, Wisconsin, and Iowa, while 17 

 are known to occur in New York and Ottawa. 



On comparing the 54 widely distributed species with those from 

 definite stages in Minnesota, it is seen that 10 are also found in Birds- 

 eye (=: Lowville), 17 in the Black Eiver, 38, or about 70 per cent, in the 

 Galena, the direct equivalent of the New York Trenton, and 11 in the 

 Cincinnatian group. 



From these figures it is evident that the stage of Silliman's Fossil 

 Mount belongs in the Galena, and that the fauna is more intimately 

 related to that of the Minnesota region than to the Trenton of New 

 York. When the New York Trenton fauna is restudied in the light of 

 recent researches in Minnesota,^ however, it will be shown that the 

 two faunas have more in common than now appears. On the other 

 hand, the lithological similarities of the Minnesota Galena and Silli- 

 man's Fossil Mount — light-colored shales predominating in both areas — 

 may explain in large measure the close identity of these widely sepa- 

 rated faunas. 



This little fauna likewise brings out the fact that the corals, brachi- 

 opods, gastropods, and the trilobites are slow in their evolutional 

 change, and the species can therefore sjDread over very great areas, 

 while the cephalopods, and particularly the pelecypods, are more sen- 

 sitive to change, and are thus restricted to localities. 



DESCRIPTION OF SPECIES. 



TJncertain Class. 

 Family RECEPTA0ULITIDJ5 Eoemer. 



RECEPTACULITES OWENI Hall. 



Eeceptaoulites oiveni Hall, Geol. Eept. Wis., 1862, p. 46, fig. 2; p. 429. — Winchell 

 and ScHUCHERT, Geol. Minn., Ill, Pt. 1, 1893, p. 57, pi. F, figs. 1-4. 



In the present collection, this species is represented by a large disk- 

 shaped specimen which measures G inches from the central apex to the 



' See the two magnificent volumes on the paleontology of the Lower Silurian fos- 

 sils of Minnesota, entitled Geology of Minuesota, III, Pts. 1, 2, published by the 

 Geological and Natural History Survey of Minnesota, N. H. Winchell, State 

 Geologist. 



