Ch. XXYI.] 



DEVONIAN OF EUSSIA. 



425 



Among the Trilobites of this era a large species of Homalonotus (fig. 

 565) is conspicuous. The genus is still better known as a Silurian form, 

 but the spinose species appear to belong exclusively to the " Lower De- 



vonian. 



With the above are associated many species of Brachiopods, such as 

 Orthis, Leptcena, and Chonetes, and some Lamellibranchiata, such as 

 Pterinea ; also the very remarkable fossil coral, called Pleurodictyum 

 problematicum (fig. 566). 



Fig. 565. 



Fig. 566. 



Pleurodictyum problematicum, Goldfnss. Lower 

 Devonian ; Dietz, Nassau, &c. 



Obs. Attached to a worm-like body (Serpula). 

 The specimen is a cast in sandstone, the thin ex- 

 panded base of the coral being removed, and ex- 

 posing the large polygonal cells ; the walls of these 

 cells are perforated, and the casts of these perfora- 

 tions produce the chain-like rows of dots between 

 the cells. 



Homalonolus armatus, Burmeister. Lower 



Devonian ; Daun, in the Eifcl. 

 Obs. The two rows of spines down the body 



give an appearance of more distinct triloba- 



tion than really occurs in this or most other 



species of the genus. 



Devonian of Russia. — The Devonian strata of Russia extend, according 

 to Sir R. Murchison, over a region more spacious 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 Brit- 

 ish, whereas when they consist of limestone they contain shells similar to 

 those of Devonshire, thus confirming, as Sir Roderick observes, the con- 

 temporaneous origin previously assigned to formations exhibiting two very 

 distinct mineral types in different parts of Britain.* The calcareous and 

 the arenaceous rocks of Russia above alluded to alternate in such a man- 

 ner as to leave no doubt of their having been deposited at the same 

 period. Among the fish common to the Russian and the British strata 

 are Asterolepis Asmusii before mentioned ; a smaller species, A. minor, 

 Ag. ; Holoptychius nobilissimus (p. 414); Dendrodus sirigatus, Owen ; 

 Pterichthys major, Ag. ; and many others. But some of the most 

 marked of the Scottish genera, such as Cephalaspis, Coccosteus, Diplacan- 

 thus, Cheiracanthus, &c, have not yet been found in Russia, owing 

 perhaps to the present imperfect state of our researches, or possibly to 

 geographical causes limiting the range of the extinct species. On the 

 * Siluria, p. 329. 



