454 
ELEMENTS OE GEOLOGY. 
curring on the coast 
at Lynmouth and 
the neighborhood, 
and called the Lyn- 
ton Group (see table, 
p. 449), form the low¬ 
est member of the 
the 18 species of all 
Fig. 522. 
Spirifera mucronata^ Hall. Devonian of Pennsylvania. 
Devonian in North Devon. Among 
classes enumerated by Mr. Etheridge 
two-thirds are common to the Middle 
Devonian, but only one, the ubiquitous 
Atrypa reticularis^ can with certainty 
be identified with Silurian species. 
Among the characteristic forms are 
Alveolites suborhicularis^ also common 
to this formation in the Rhine, and Or- 
iMs arcuata^ very widely spread in the 
North Devon localities. But we may 
expect a large addition to the number 
of fossils whenever these strata shall 
have been carefully searched. The 
Spirifer Sandstone of Sandberger, as 
exhibited in the rocks bordering the 
Rhine between Coblentz and Caub, be¬ 
long to this Lower division, and the 
same broad-winged Spirifers distinguish 
the Devonian strata of North America. 
Among the Trilobites of this era sev¬ 
eral large species of Homalonotus (Fig. 
522) are conspicuous. The genus is still 
better known as a Silurian form, but the 
spinose species appear to belong exclu¬ 
sively to the “ Lower Devonian,” and are found in Britain, 
Europe, and the Cape of Good Hope. 
Devonian of Russia. — The Devonian strata of Russia ex¬ 
tend, according to Sir R. Murchison, over a region more spa¬ 
cious than the British Isles; and it is remarkable that, where 
they consist of sandstone like the “ Old Red ” of Scotland 
and Central England, they are tenanted by fossil fishes often 
of the same species and still oftener of the same genera as 
the British, whereas when they consist of limestone they con¬ 
tain shells similar to those of Devonshire, thus confirming, 
as Sir Roderick has pointed out, the contemporaneous origin 
which had been previously assigned to formations exhibiting 
two very distinct mineral types in ditferent parts of Britain."^ 
* Murchison’s Siluria, p. 329. 
Homalonotus armatus, Bnr- 
meister. Lower Devoni¬ 
an; Daun, in the Eifel; 
and S. Devon. 
Obs. The two rows of spines 
down the body give an ap¬ 
pearance of more distinct 
trilobation than really oc¬ 
curs in this or most other 
species of the genus. 
