412 NEW YORK STATE MUSEUM 
of these fossils and possibly also graptolites that would indicate the age 
of the beds. They have indeed afforded a layer with an association of 
finely preserved seaweeds, the eurypterids herewith described, and the 
following graptolites: Dicellograptus gurleyi Lapworth, 
Climacograptus bicornis Hall, Climacograptus 
bicornis var. peltifer Lapworth, Cryptograptus tri- 
cornis (Carruthers), the first three forms in great abundance. This 
graptolite association 1s one of undoubted Normanskill age. The sea- 
weeds occur in large perfect fronds' and are of the same type as those in 
the Schenectady shale. The eurypterids also are strikingly similar to those 
from the Schenectady beds. 
In one case (Pterygotus ? nasutus) we have been unable 
to distinguish the Schenectady and Normanskill types. This striking 
similarity of the two faunas (one of Chazy, the other of Trenton age) 
amounting almost to identity, seems to indicate a very slow progressive 
development of the eurypterid faunas, probably owing to their early 
1 More or less shapeless patches of these seaweeds and possibly also of eurypterid 
integument from the Normanskill shale at Kenwood near Albany were described by 
R. P. Whitfield [Am. Mus. Nat. Hist. Bul., v. 1, no. 8, 1886, p. 346, pl. 35] as Rhom- 
bodictyon and referred to the sponges on account of an apparent spongelike fibrous 
structure consisting, according to Whitfield, of two or three sets of rods, the principal 
¢é 
ones of which are “ straight, rigid and apparently cylindrical.’ This peculiar struc- 
ture is shown by all the thicker specimens from the shale of the Broom street quarry 
and is there obviously only a system of parallel shrinkage or cleavage cracks found 
wherever the carbonaceous films become rather thick; and is entirely independent of 
outlines of the fossil but strictly parallel on all fossils of the same slab, thereby indi- 
cating its connection with a latent cleavage of the folded beds. The parallel main 
cracks are connected by more irregular cross cracks, the whole forming a very decep- 
tive pattern. Sometimes these cracks have become secondarily filled by calcite or 
pyrite and the carbonaceous matter subsequently destroyed, whereby an apparent 
spongelike system of rods has resulted. Inspection of Whitfield’s types in the Amer- 
ican Museum of Natural History has shown that the types of the two species of Rhom- 
bodictyon are of quite the same nature as the thick carbonaceous patches of seaweeds 
from the shale at Catskill. 
