SILURIAN FOSSILS OF RUSSIA. 
37* 
exhibits, however, such remarkable variations in the eyes, probably due to the 
greater or lesser age of the individual, that we take this opportunity of also figuring 
a second example (3), in which the eyes project from the head to about four-tenths 
of an inch ; and thirdly, a case of extreme projection of this member in figure 1, 
which represents a very remarkable specimen of the Asaphus cornutus' (Pander). 
We have already said that the Asaphus Buchii and A. lieros (Dalm.) (or tyrannus, 
Sil. Syst.), so abundant in England, seem gradually to disappear in the eastward 
range of the deposit. They are consequently very rare in Russia. 
Among other Trilobites of this age, Professor Eichwald speaks of the Asaphus 
Vulcani, a species found in the Lower Silurian rocks of England, and we ourselves 
recognised the Calymene Downingice , which is a Dudley fossil. The occurrence of 
the latter is by no means hostile to our views of classification, for we now know that 
the Calymene Blumenbachii, which in England is most abundant in the Ludlow 
and Wenlock formations, there descends in some places into the Caradoc sandstone. 
The occurrence of a few of the same species in the Lower and Upper Silurian 
deposits, is indeed just what may be looked for in a system, which, on the whole, 
is characterized by a general community in its organized beings. Thus there are 
certain shells as well as crustaceans which are common to the conterminous forma- 
tions of the lower and upper groups in Russia, Scandinavia and England, and of 
these we may cite the Leptcena depressa and Terebratula reticularis ; shells which 
having a very wide geographical distribution, are found to have also an extensive 
vertical range ; or, in other words, to have continued longer in existence than their 
congeners, in accordance with a law to which w r e formerly directed the attention of 
geologists 2 . But here we must observe, that the Silurian rocks of Russia hold their 
place well in the general series of palaeozoic life, and bear a strong resemblance to 
their equivalents of Western Europe 3 , in containing a large proportion of Orthidae 
In addition to the work of Pander, in which many structural details of the Russian Trilobites are given, 
we have already referred our readers to the ‘ Silurischen Schichten ’ of M. Eichwald, and to a recent 
memoir by His Imperial Highness the Duke of Leuclitenberg. 
1 We owe these specimens, which so clearly exhibit the transitions in the length of the eye and the 
variations between Asaphus expansus and A. cornutus, to our friend Dr. Worth, who detected them in 
the ravines of the Pulkovka brook. The caudal portion (2 of woodcut) is identical in all the varieties ; 
and after examining a great number of individuals which exhibit various shades of transition, we confess 
that we think the A. cornutus (Pand.) is only a variety of A. expansus (Dalm.). 
2 See Trans. Geol. Soc. of London, vol. vi. p. 335. 
3 Among the shells common to the Lower Silurian rocks of Scandinavia and Russia, we must further 
mention Euomphalus qualteriatus, Orthis valUgrumma, 0. testudinaria, Leptcena sericea, Spiri/er poram- 
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