686 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



Cornwall, and of Baggy, in Devonshire. As before stated, we have no 

 means of establishing- any real comparison between the 43 genera 

 and 113 species of Eish that are known to be in the trne Lower, 

 Middle, and Upper Old Eed Sandstone of Scotland, England, and 

 Wales &c. 



The typical Upper Devonian beds of Petherwin yield Cypridina 

 serratostriata, the only form of bivalve Crustacean (Ostracoda) 

 known in the Marine Devonian beds. It is the Ehenish species, 

 and occupies the same position in our English Upper Devonian of 

 JN'orth Cornwall as in Nassau, Thuringia, and Eraiiconia ; its abun- 

 dance and persistency, accompanied also by the genus Clymenia, 

 affords a parallelism which cannot be overlooked, other conditions 

 also coinciding. 



The Trilobita, as contrasted with the Silurian species, afford no 

 comparison ; they, like the Corals, are a group of genera and species 

 peculiar to the Devonian rocks which contain them. I^o genus or species 

 occurs common to the Carboniferous and Devonian rocks. It should 

 be noticed also that although the 6 genera, viz. Bronteus, Cheiriirus, 

 Harp&s, Homalonotus, Phacops, and T rimer ocephalus are Silurian, 

 yet their 11 species are all peculiar to Devonian strata ; and although 

 Phacops granulatus, P. laciniatus, and P. latifrons occur in the 

 upjDcrmost Devonian beds, they have, nevertheless, never been found 

 in the Carboniferous series, unless it be admitted that the Barn- 

 staple beds are positively of that age, and P. latifrons occurs in 

 them. This affinity with the Silurian series through the Trilobites 

 adds one other element to strengthen the view that difference of 

 province, migration to new areas, nature of sea-bottom &c., or the 

 remnant of an older and almost extinct fauna might have existed 

 during the series of changes which took place, even over so small a 

 geographical area as that occupied by the Silurian and succeeding 

 Devonian seas, at, or contemporaneous with, the close of the Silu- 

 rian period and the commencement of the Devonian. These genera 

 and species of Trilobites died out at the close of the Devonian 

 period, and were replaced by one family only (the Proetidse), pos- 

 sessing three new generic types, which characterize the Carboni- 

 ferous rocks, viz. Phillipsia, GynffitJiides, and Bracliymetopus, which 

 contain 15 known species ; so that neither families, genera, nor spe- 

 cies of this group passed from the Devonian to the Carboniferous 

 sea* . The remaining seven genera in the orders Merostomata or 

 Poecillopoda, and their nineteen species, found in the Old Bed Sand- 

 stone have no significance in our present inquiry and examination, 

 arising from want of comparison and our not yet being able to 

 satisfactorily correlate the group of the marine Devonians with the 

 received divisions of the Old Eed Sandstone. 



4. CepJialopoda. — Comparisons amongst the chief Devonian 

 genera and species themselves, or between them and those of 

 the formations above or below them, would not be complete 



* The distribution of this order, both stratigraphically and chronologically, is 

 the same through and over the three European areas, the same results being ob- 

 served in the Rhenish, Eifelien, and Boulonnais rocks. 



