44 
the articulations of the middle lobe, “ are sometimes 
simple or undivided, at least in. the post abdomen, 
but that they are always bifurcated in the Calymene. ” 
As far as our observations have extended, these re- 
marks do not apply either in the one case or the 
other. 
The head or buckler of the Asaph, is not so Salant 
divided into three lobes as the Calymene; they are, 
_ however, quite distinct. The oculiferous tubercles — 
are in some species exceedingly well marked by a re- 
ticulated structure. 
This genus often occurs at the same localities with 
the Calymene, though in some instances it seems to 
occupy rocks peculiar to itself. Dr. John Bigsby, in 
his list of organic remains occurring in the Canadas, 
states, that he never found a single species of the 
genus Calymene, on the north side of the River St. 
Lawrence, although the Asaphs were very abundant.* 
In his Sketch of the Geology of the Island of Mon- 
treal, he however observes: “ Of Trilobites, the 
Asaph genus is the most abundant, they approach 
nearest the species caudatus, of Brongniart. I have 
found no entire Calymene, but many bucklers or heads 
of the Blumenbach species, some of them an inch 
and a half in diameter. They are found whole in 
considerable numbers in the vitae of Quebec.’”’} | 
* Silliman’s Journal, vol. viii. p. 83. | 
t Annals New York Lyceum, vol. i. p. 214. 
