522 NEW YORK STATE MUSEUM 



Of these however, Pholidops subtruncata, Modio- 

 lopsis modiolaris and Aparchites minutis* 

 s i m u s present varietal differences. Pholidops sub- 

 truncata does not possess the faint median angulation of the 

 Lorraine form, and has besides, been found in the Canadian 

 Trenton by Ami ; Modiolopsis modiolaris has the back 

 and base nearly parallel and thus approaches Ulrich's M. s u b - 

 recta, or is identical with one of the Utica varieties, men- 

 tioned by this author; and also the Aparchites minutis- 

 s i m u s approaches the Trenton variety by the absence of the 

 subcentral projecting point. 



The Lorraine element is, h^nce, by no means, so strongly repre- 

 sented in this Utica fauna of Mechanicsville as appears at first 

 glance or as it is in the Utica shales of Green Island. This is 

 still more emphasized by the absence of Cleidophorua 

 planulatus, Cyrtolites ornatus and Lyrodesma 

 pulchellum, while, on the other hand, the Trenton element 

 is so strong that the beds almost assume the character of tran- 

 sitional beds between the Trenton and Utica terranes. 



An important and novel factor in this fauna is the peculiar 

 Olimacograptus caudatus which occurs frequently 

 and in large specimens. This striking type of graptolite structure 

 was first described by Lapworth from the Hartfell shales of Scot- 

 land which are considered homotaxial with the upper Dicello- 

 graptue zone of Canada, from which the same graptolite has been 

 reported. As it is restricted to the upper Dicellograptus zone, 

 and, therefore, is a valuable index fossil, ite occurrence in the 

 lowest Utica shale of Mechanicsville is of significance, indicating 

 the presence of this zone in the Hudson river region and its prox- 

 imity to the lowest Utica. If we add, that also D a w s o n i a 

 campanulata, found at Mechanicsville, and Crypto- 

 graptus tricornis, found in similar lower Utica beds on 

 Van Schaick island (see station 8) are fossils of the Dicellograptus 

 zones, and not of the Utica horizon, it can be concluded with 

 some degree of certainty that the upper Dicellograptus zone, 

 when present in the Hudson river valley, directly underlies the 

 Utica terrane, that is, is homotaxial with the whole or part of the 



