ETHERIDGE — DEyO>'IAX EOCKS A>'D FOSSILS. 665 



in these four areas *. Four species of one genns are kno'svn also 

 in the Eussian Devonians, viz. the -widely distributed and charac- 

 teristic Favosites Goldfv.ssH, F. reticulata, F. fibrosa, and F, cer- 

 vicornis {polymorijlia). 



It is needless attempting any comparison of the British Devonian 

 corals with the Carboniferous ; for they stand alone, one species 

 only, Alkhelinia antiqua, M^'Coy, with much doubt being referred 

 as common to the Upper Devonian series of Xorth Devon and the 

 Carboniferous beds of Hook &c. in the South of Ireland. 



Comparisons made amongst the Devonian Ccelenterata (Tables II., 

 Y., & YII.) reveal to us the importance that must be attached to the 

 intermediate grouping and stratigraphical place of the South and 

 North ^Middle Devonian limestones and slates, the limestones of both 

 areas yielding, as in all others, the chief mass of the species ; but 

 Petraia celtica, P. gigas, P. j^leuriracUalis, and Pie nor od id yum pro- 

 hlematicinn are abundant in the slates, and Favosites cervicornis is 

 common to both, in Xorth and South Devon. 



The relation of the two allied and connected regions is shown 

 from the fact that they contain 10 genera and 18 species of corals 

 in common, an agreement singularly close to that borne by the three 

 European areas to our own, where the same number of genera occur, 

 and 22 species (see Tab. Y.). This coincidence may not have any 

 great value in itself, but it tends to show the persistency and 

 distribution of species through a given time, and over a definite 

 area. Xo species is known to be common to the Lower, Middle, 

 and Upper series, and only one to the Lower and Middle, viz. Favo- 

 urites cervicornis. Xo attempt need be made to individualize special 

 genera or species, as the Devonian corals as a group are peculiar to 

 the beds in which they occur, and distinctly mark the intermediate 

 character of the Devonian series, as well as, being a zoological 

 group, distinctly characterizing the Middle Devonian series, to which 

 they are confined. 



3. Crustacea. — This class, as a whole, is but feebly represented in 

 the marine Devonian group, two orders only being known, viz. the 

 Ostracoda and Trilobita. Our present means of comparison between 

 the Old Eed Sandstone proper and its believed equivalents, the 

 Lower, ^Middle, and Upper Devonian of Cornwall and Devon, both 

 on physical and pala^ontological grounds, do not enable us to affirm 

 positively that they are identical ; but it is not a httle singular 

 that two such opposite classes in the animal kingdom as the Crus- 

 tacea and Fish should be so largely represented at the close of the 

 Silurian and commencement of the Old Bed Sandstone period, 

 the former through the suborder Eurypterida (order Merostomata) ; 

 the latter through the Ganoid and Placoid Eishcs, both of which, 

 and the species in which, equally represent the close of one period 

 and the commencement of the other, the one (Merostomata) not 

 again appearing in the Devonian rocks of any area, whilst the 

 Fishes are only sparingly represented in the Middle Devonian of 

 Livonia, in Kussia, of the Eifel, in Ehenish Prussia, of Looe, in 

 * Devonshire, Ehenish proTinces, Belgium, and France. 



