Geological Society. 209 



has been detected, a distinct family from the Cephalaspidae, which 

 exhibit that structure. 



He then proceeded to correlate the American beds yielding Palce- 

 aspis with the Ludlow beds of England. The American fish were 

 chiefly found in the Bloomfield Sandstone at the top of the middle 

 division or variegated shale of the fifth group of Rogers. This 

 fifth group of the Pennsylvania^ Survey immediately underlies the 

 Water-lime, corresponding to the English Lower Ludlow, and has 

 been shown by the writer to represent the Onondaga shale of JNew 

 York. The position of the latter in the series is shown by the fol- 

 lowing sections taken from Prof. James Hall : — 



New York. Great Britain. 



Lower Helderberg Wanting. 



Water-lime Lesmahago beds. 



Onondaga salt group Wanting. 



Niagara group Wenlock Limestone. 



The last two were considered representative by Sir P. Murchison, 

 and this view has never been disputed. 



It therefore appears that the Pennsylvanian Pteraspids from the 

 Bloomfield Sandstone are older than Scaphaspis ludensis of the 

 Lower Ludlow by the time required for the deposition of 200 feet 

 of strata. But 1000 feet below the horizon just named commi- 

 nuted fish-scales are found in beds containing Leperditia alta ; and 

 again, 700 feet lower, in the iron sandstone near the middle of the 

 Clinton group, which corresponds to the English Upper Llandovery 

 beds ; and 200 feet below the Ore Sand-rock, broken plates, with 

 the superficial striation of Palceaspis and a few fine spines of 

 Onchus (described as O. Clintoni) are met with. The horizon is 

 well defined, for the Ore Sand-rock contains Beyrichia lata, Calif mene 

 Clintoni, Ormoceras vertebratum, and other characteristic fossils. 

 The iron sandstone also contains white pellets, apparently of copro- 

 litic origin, and containing 32 per cent, of phosphate of lime. 



Previously reported discoveries of fish in American Silurian rocks 

 were discussed, and their supposed age shown to be erroneous. The 

 paper concluded with the description of two species of Palceaspis 

 (P. americana and P. bitruncata), of Onchus pennsylvanicus from the 

 Bloomfield Sandstone, Onondaga group, and of Onchus Clintoni from 

 the iron sandstone of the Clinton group. 



2. " Notes on species of Phyllopora and Thamnis us from the 

 Lower Silurian Pocks, near Welshpool, Wales." By George Robert 

 Vine, Esq. (Communicated by Prof. P. Martin Duncan, F.R.S., 

 F.G.S.) 



In this paper a species of Phyllopora from the Caradoc beds of 

 Wern-y-scadog, Llanfyllin. was described as P. tumida, and a Tham- 

 niscus from the volcanic ash of Middleton Hill, near Welshpool, 



Ann. & Mag. N. Hist. Ser. 5. Vol. xv. 19 



