51 
MEROSTOMATA. 
Another form of Crustacea less common than the Trilobites, 
but quite as remarkable, is that of the Eurypteroids (broad 
wings), a group not known until the Medina epoch. They appear 
to have flourished in highly salt waters, and must have been quite 
abundant in the seas which covered central and western New 
York during the deposition of the rocks of the Onondaga Salt 
group, under which epoch there is a large and beautiful collec- 
tion of them exhibited. See Case r, Sect. 8, and in Alcove Case 
5 ; perhaps the finest collection of type specimens of these 
fossils in existence. They also 
flourished in the Catskill period, 
but in this country are very 
scarce, only a single head of a 
very large species having been 
found ; while in Scotland they 
were numerous and of gigantic 
proportions; some of their frag- 
ments indicating a length of 
nearly twelve feet. They appear 
again in the Coal Measures in 
Fig. 38.— F.urypterus remipes. Pennsylvania and in Illinois ; a 
single individual from the latter 
state be.ng on exhibition in Case o, Sect, r i. 
There are a few other forms of articulates scattered through 
the collection, but none of great interest, except to specialists. 
SUB-KINGDOM VERTEBRATA. 
FISHES. 
The fishes of the Palaeozoic ages were either Ganoids, like the 
Oar-pikes, their surfaces covered with strong enameled or plate- 
like scales ; Placoderms, the heads and sometimes the bodies of 
which were coated with strong bony plates ; or Sharks. They are 
mostly represented as fossils by detached teeth, jaws, plates, fin- 
spines or scales. Occasionally entire specimens of ganoids are 
found in the Devonian and Carboniferous, but are not common. 
In the Mesozoic and Cenozoic ages other forms are found, es- 
pecially the bony fishes, Teliosts. 
