114 GEOLOGICAL MEMOIRS. 



Bogoslofsk ill the Ural. Of the genus Phacops, we have from Rus- 

 sia only the P. DowningicB (^Calymene auct.), to which we ought 

 perhaps to restore the name of macrophthalma given by M. Bron- 

 gniart*. This species, which has been long known as occurring in 

 the Dudley limestone, is common to both divisions of the Silurian 

 series. In addition to this, P. macrophthalma of authors ( Calymene 

 latifrons of Bronn) has also been mentioned as amongst the fossils 

 from near St. Petersburg ; but we greatly question whether this 

 species, common to the Devonian and Silurian series, descends into 

 the lower members of the latter, although, from an indifferent speci- 

 men brought by M. Tchihatcheff, it appears to exist in the Altai. 

 Lastly, amongst the St. Petersburg Trilobites we may mention Am^ 

 pyx nasutus and three species of the genus Metopias, established by 

 M. Eichwald. Two of these are well known in Sweden and Ireland 

 under the names Trilobites sphcBricus and Nuttainia hihernica. 



While most of the Trilobites which generally characterise the 

 Devonian system are absent in Russia, we find in tolerable abun- 

 dance in the carboniferous beds, two species of the genus Phillip- 

 sia, one of the last forms under which the family of Trilobites pre- 

 sented itself before its final extinction. 



It will appear from what has been said above, that most of the 

 Russian Trilobites are concentrated in the lower members of the 

 Silurian series, where we have observed ten species, viz. Calymene 

 Fischeri, C, Odini, C. hellatula, Asaphus expansus, IllcEnus crassi- 

 Cauda, Phacops Downingice, Metopias aries, M. Hilbneri, M. coni- 

 ceps and Ampyx nasutus. We may also add, Jirst, that all these 

 species are characteristic of the lower members of the Silurian series, 

 except Phacops Downingice, which occurs also in the Dudley lime- 

 stone and even in the limestone of Ferques ; and secondly, that all, 

 with the exception of M, coniceps, occur both in Scandinavia and 

 in the British Islands at precisely the same geological horizon. 



We have nothing more to add on the subject of the Trilobites 

 observed in the course of our rapid traverses through the country. 

 The number of species mentioned in our list as observed by other 

 authors, no doubt proves that our collections are very incomplete; 

 but it is also possible that the same species found in detached frag- 

 ments may have received different names, and that the whole num- 

 ber may thus have been increased without sufficient ground from 

 actual investigation!. 



Fishes. — It is well known that the most diligent research has failed 

 in discovering any traces of these animals amongst the earliest strata 



* Hist. Nat. des Crust. Fos., p. 15. In his plates M. Erongniart has confounded 

 two distinct species under the name Calymene macrophtlialma^ but it is easy to 

 satisfy oneself that his description apphes to the species now commonly caJled 

 C. Downingice. 



t To obtain an idea of the actual state of our knowledge on the subject of Tri- 

 lobites, M. Burmeister's beautiful work, * Die Organisation der Trilobiten,' must 

 be referred to. More than fifty genera and upwards of 200 species are there de- 

 scribed. [An English edition of this work, with impressions from the original 

 plates, and enriched with much additional matter by the author, has recently ap- 

 peared among the publications of the Ray Society* — Ed.] 



