261 



genera found in the Erere beds, but even species of those same 

 genera, which cannot be separated from North American species of 

 the Hamilton gronp. 



Spii'ifera Pedroana, so abundant at Erere, seems to represent, not 

 a single species of the Devonian, but several, which form a scries 

 extending through the Corniferous and Hamilton groups. The 

 different species of this series are very distinct from one another in 

 their extreme forms, but they are so connected by intermediate 

 varieties, that they present a good subject for the study of develop- 

 ment. The series includes in North America S. varicosa and S. 

 macra of the Corniferous, and ^S*. mediaUs, S. macronoia and ;iS'. 

 angusta of the Hamilton. Streptorliynclius Agassizii, the most 

 abundant fossil at Erere, belongs to that transition group of the 

 Streptorliynchi which helps to characterize the Devonian ; yet, so far 

 as at present known, the new species does not attain the large size 

 of the Devonian species of that genus elsewhere. The genus Yitu- 

 lina has been known by only a single species, which is confined to 

 the Hamilton group of New York, and was considered rare, but 

 somewhat recently it has been found in greater abundance. The 

 Erere form does not differ from the larger varieties of V. pustulosa. 

 Hall, of the Hamilton group. The Erere Tropidoleptus is identical 

 with the uncarinate forms of T. carinatus from the Hamilton 

 group of New York. Though only a very few specimens of PJiyn- 

 clionella have been obtained from Erere, there is little difficulty in 

 uniting them with R. dotis of the Hamiliou. The geniis Clionetes 

 is represented by several species, all of which are closely related to 

 Hamilton group species of New York. The single species of Dis- 

 cina, and one of the species of Lingula, are probal)ly only varieties 

 of North American Hamilton group species. It may appear strange 

 that many of the most common genera found in the Devonian, 

 such as Atrypa, Stropliodonta, Productella, etc., are wanting, while 

 more obscure genera are abundantly represented ; but when we con-' 

 sider that the collections were made over an area of only a few feet 

 in extent, and from a thickness of but a few inches, we must see 

 that it is just what might be expected. 



