BRACHIOPODA. 159 



Niagara species Orbicula ? squamiformis, though without further definition, hut 

 in Volume III of the Palaeontology, published the same year, the genus was 

 illustrated and defined under the name of Pholidops, the term Chaniops being 

 unaccountably overlooked. 



The relations of this genus to Pseudocrania, McCoy, and Pal^ocrania, 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 tlie forni.s belonging to widely 

 separated faunas, e. g., P. Trentonensis, P. Cincinnatmsis, P. squamiformis, P. ovata, 

 P. HamiltonicR 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. 



