EARLY DEVONIC HISTORY OF NEW YORK AND EASTERN NORTH AMERICA 131 



quite small but the first two lobes are fused at the outer edges. The genal 

 spines are produced, the eyes furrowed at their base and the groove within 

 the border is conspicuous. The border in front is produced into a bifurcate 

 process, the branches of which are flat, very divergent and rise from a broad 

 base. We have noted that one of the specimens of the Perce species, 

 Probolium biardi shows, probably by accident only two instead of 

 the normal three branches of the snout but this difference is unaccompanied 

 by any other structural departure in the shields and it has been observed but 

 once. The aspect of the cephalon before us is very unlike that in the various 

 details referred to. Dalmanites (P.) nasutus Conrad' is a bifurcate 

 species in the Helderbergian (New Scotland beds) of New York, which has 

 more in common with P. esnouf i, specially in its smooth border, but the 

 base of its snout is very much more elongated and its branches slender and 

 cylindrical. Though as yet we know but little of P. esnoufi, its pres- 

 ence here is of very great interest. The specimen measures in length, from 

 tip of snout 32 mm, from front of glabella 23 mm and in width 50 mm. 



Locality. In the cherty beds of the series between Grande Greve and 

 Little Gaspe. 



Species name. Esnouf, a well known Jersey surname on the Forillon. 



OBSERVATIONS ON THE DALMANITES OF THE EARLY DEVONIC 



No feature is more significant of the early stages of boreal Devonic 

 faunas than the decline of Dalmanites expressed in concomitant development 

 of cuticular excrescences. We have here portrayed a number of illustrations 

 of these evidences of race debility and their occurrence is widespread. Sub- 

 generic divisions have been founded on them and though these must, by the 

 nature of the case, be of fugitive value yet they serve a purpose in efforts at 

 correlation. These excrescential developments affect the head and tail 

 shields chiefly, that is the stable or unmovable parts in contrast to the 

 mobile parts of the thorax. It is to be noted that such modifications do not 

 involve these parts in equal degree for a species with ornamented cephalic 

 integument usually has the pygidium devoid of such traits ; and the converse 

 is quite as true. Species of Probolium, for example, in which the anterior 

 border is produced into a long proboscis have a simple tail shield with a 

 longer or shorter axial spine ; on the other hand the genus Coronura, in 

 which the tail is grotesquely ornamented in such form that the posterior 

 extremity is divided and turned up into an erect collar prolonged into spines, 

 has a cephalon with no dermal extravagances and quite in keeping with the 

 typical expression of the Lower Siluric representatives of the genus. 



We may observe that the accession of these dermal excesses accom- 

 panies the final appearance of other trilobite genera, but nowhere with such 



' Palaeontology of New York, 3 : 362, pi. 76, fig. 1-8. 



