BRACHIOPODA. 
159 
Niagara species Orbicula ? squamiformis, though without further definition, but 
in Volume III of the Palaeontology, published the same year, the genus was 
illustrated and defined under the name of Pholidops, the term Craniops being 
unaccountably overlooked. 
The relations of this genus to Pseudocrania, McCoy, and Pal^eocrania, Eich- 
wald, have been elsewhere discussed. 
Species of Pholidops are often abundant in American palaeozoic faunas, their 
first appearance being, as already noticed, in the Trenton, and their latest 
known representative in the Bedford shales. It has already been observed that 
there exists a close specific similarity in some of the forms belonging to widely 
separated faunas, e. g., P. Trentonensis, P. Cincinnatensis, P. squamiformis , P. ovata, 
P. Hamiltonia and P., sp. (?), from the Trenton, Hudson, Niagara, Lower 
Helderberg, Hamilton and Waverly groups respectively, but it is indispensable 
to recognize them as distinct species. In strong contrast to this general preva¬ 
lence of Pholidops in America, is the evident paucity of its representation in 
Europe, where occur only the P. implicata, in England, and the same species 
with P. antiqua , in Gotland, the former being regarded by some authors as 
synonymous with the latter. 
