478 GEOLOGY. 



dent southern Hamilton fauna, (2) the invading northwestern fauna, 

 and (3) the shallow and rather turbid waters in which these faunas 

 met and merged. 



The last of these factors expressed itself in a notable rarity of corals 

 to which the impurity of the waters was uncongenial. In a lesser 

 degree, this was true of the crinoids, but they none the less exhibited 

 rather surprising powers of resistance or of adaptation, since all the 

 orders were represented. Cystoids and blastoids have not been found, 

 and starfishes were rare. The first known American echinoid appeared 

 in the Chemung, though in Europe the type had appeared as early 

 as the Ordovician. 



The brachiopods best express the outcome of the commingling of 

 the resident and immigrant faunas. They distinctly indicate two 

 groups: (1) an indigenous class which had developed from the pre- 

 ceding resident fauna of the basin; and (2) an exotic class which 

 was derived from the immigrants and bore European characters. 

 Among those of native descent were Atrypa reticularis, Atrypa hystrix, 

 Cyrtina hamiltonensis, Tropidoleptus carinatus, and probably certain 

 species of Stropheodonta and Productella. Among the prominent immi- 

 grants were those previously discussed and illustrated in Fig. 212. 

 The foreign group was more conspicuous than the native. The reverse, 

 however, was the case with the mollusks. The pelecypods were numer- 

 ous, but not so abundant as in the preceding epochs. The majority 

 appear to have been descendants of the resident bivalves. Distinct 

 foreign relationships have not as yet been satisfactorily distinguished, 

 though some suggestive resemblances have been noted. Perhaps 

 the bivalves were not well suited to distant migration. The gastro- 

 pods were less numerous than before, and apparently local. The 

 |)teropods were represented by Tentaculites and Conularia, similar to 

 those of the preceding faunas. The genera of the cephalopods were 

 usually the same as those of the southern Hamilton, though the species 

 were mainly new; but in the goniatite genus Manticoceras, which is 

 highly characteristic of certain Portage beds in western New York, there 

 was a conspicuous Eurasian immigrant element from the northwest, 

 as notable as that of the "cuboides" fauna. 1 



The marine fishes of the late Devonian are not very abundantly 

 represented in present collections, and can only be characterized with 



1 J. M. Clarke, 16th Ann. Rep. N. Y. St. Geol. for 1896, pp. 22-161. 



