OF SILUEIAN AND DEVONIAN. 61 



of the correctness of tlie outline at that part. If a crustacean, the head has more affinity 

 to that of the Synxiphosuridae than the Eurypteridse, as may be seen by comparison with 

 Exapinurus and Pseudoniscus ; and this relationship is also better borne out by the 

 tapering caudal segment. 



But, on the other hand, if we consider the union of the two rings which compose 

 the first segment of the thorax, the absence of pleurae and the probable possession of a 

 pair of large limbs attached to the last segment of the headshield we observe characters 

 which mark the Eurypteridse. Neither Eurypterus nor Pterygotus, however, had a crust 

 similar to this species, and it differed from both in its minute size and probable fresh- 

 water habitat. The size corresponds better to the Synxiphosuridae. 



This organism was found among fragments of plants that show scarcely any marks 

 of maceration, and which have rare insect remains scattered through them ; it might, 

 therefore, be surmised that it has been the larva of some insect, such a larva, for instance, 

 as some water-beetles have,' and with this the small size of the object, and also that of 

 its anterior segment, agree ; but the division of the body segments into two regions and 

 the probable presence of limbs are objections. 



On the whole it appears more correct to regard this organism as a type of fresh-water 

 crustacean intermediate between the Euryiiteridse and the Syiixiphosuridaj. 



Geological Age of the Insect Remains. 



This was determined some years ago by Sir J. "VV. Dawson upon the evidence 

 afforded by the plant remains of the beds in which these insects occur. From the first 

 collections made. Sir William supposed the age to be Upper Devonian ; but his more 

 mature opinion, based upon the study of the large collections made by the late Prof. 

 C. F. Hartt and myself from these beds, and placed in Sir William's hands for study, and 

 of collections from Gaspé, etc., was that these plants were of Middle Devonian age. The 

 following descending series, in which unconformities are marked by a dividing line, show 

 their relative position in the Devonian system. 



Of these divisions the Bloomsbury conglomerate is variable in thickness, and not 

 known in the central counties. The break between the Cordaite Shales and Misiiec 

 series is most clearly shown in Charlotte Coiinty, where this series rests upon the Silurian, 

 and has boulders composed of the fossils of the Silurian. The second uucomformity is 

 shown in the same county by nearly horizontal Perry sandstone resting uiDon highly 

 inclined Mispec conglomerates. The three series represent a great lapse of time, probably 

 the whole Devonian Age. 



Perry Sandstones, with Upper Devonian flora, according to Sir J. W. Dawson, but lithologically 

 resembling the Lower Carboniferous Sandstone. 



Mispec Conglomerate and Slate. 



03 a 

 Q 



Cordaite Shales and Flags, Middle Devonian flora. Insed remains (in oldest beds of the Cordaite 



shale.) 

 Dadoxylon Sandstone (with an older Devonian flora, G. F. M.) 

 Bloomsbury Conglomerate, etc. 



See larva of Elmis in Packard's Guide to Insects, p. 450. 



