^1^ PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



his visit to Scotland in 1834, not more than four species were 

 known. Five years afterwards, when Sir R. Murchison published 

 his ' Silurian System,' ten genera and seventeen species of fishes, and 

 fifteen genera and twenty-three species of mollusca are enumerated 

 by him as belonging to the middle and lower Devonian beds. In 

 the recent work on Russia, M. de Verneuil enumerates forty-six 

 species of fishes and sixty-six species of mollusca, which he and his 

 fellow-travellers found in the same group in that country. M. 

 Agassiz, in his ' Monograph of the Fishes of the Devonian System,' 

 raises the number of genera to forty-three, and of species to 105, 

 belonging to six or seven families; and he tells us that Monte 

 Bolca itself, hitherto reported to be the locality of all others most 

 rich in species of fossil fishes, does not contain a greater number ; 

 adding, that as only a comparatively small portion of the rocks of 

 this system has been examined, many additions may be expected. 

 M. Agassiz is shortly going, it is said, to North America, where he 

 will very likely discover many new forms. It is gratifying to find 

 him ascribing the main success of his researches in this field " aux re- 

 cherches perseverantes et au zele infatigable des geologues Anglais." 



But not only is there this great variety of genera and species, but 

 the number of individuals found in some localities is inmiense. 

 Thus in some parts of Russia there are breccias almost wholly com- 

 posed of the scales and plates of the Asterolepis, and the remains of 

 the Pterichthys are so abundant in the geodes of Lethen Bar in 

 Nairnshire as to have been collected in cart-loads. But our wonder 

 is not alone excited by the great variety and number of vertebrate 

 animals of a high organization in strata so very low in the order of 

 formations ; there are many most remarkable features in the history 

 of this early part of the animal creation which the researches of M. 

 Agassiz have brought to light ; for these however I must refer you 

 to the work itself. 



M. Agassiz, in speaking of the lowest beds in which the remains 

 of fishes have been found, makes the following important observa- 

 tions on the probability of their existing in still lower beds : — " If 

 we have not yet been able to recognize remains of fishes below the 

 Lower Ludlow rocks, I do not think that we ought from that to 

 conclude that fishes do not exist even in the oldest of the fossilife- 

 rous beds ; for their extraordinary abundance in the Devonian se- 

 ries, and the distinct recognition of them in certain Silurian beds, 

 where, it is true, they are but imperfectly preserved, suflficiently in- 

 dicates that on its first appearance that class of animals was contem- 

 porary with the development of the types of all the classes of in- 

 vertebrate animals." 



Mr. Lyell states that the lowest rock in which ichthyolites have 

 been traced in America is the Clinton group, which may be consi- 

 dered the bottom of the Upper, or top of the Lower Silurian series. 

 Ichthyolites have recently been found in the Wenlock shale ; an- 

 other step in descending order, and so far in support of M. Agas- 

 siz's views. 



