102 
GEOLOGY OF THE FOURTH DISTRICT. 
3. Calymene Niagarensis. — The middle lobe of the head of this trilobite is marked by 
three rounded protuberances on each side ; the front one very obscure, and sometimes scarce¬ 
ly distinguishable ; the posterior one very prominent. Eyes small, not reticulated, opposite 
the central protuberance of the middle lobe. It has thirteen articulations on the back, and 
eight in the tail. The surface is entirely covered with minute rounded tubercles. 
This fossil has usually been referred to C. Blumenbachii, as well as to the species in the 
Trenton limestone ; but our fossil differs from the last, in the more rounded posterior angles 
of the buckler, and in other particulars ; from the former it differs in being uniformly of the 
small size represented, in having but thirteen articulations in the back, and in the less pro¬ 
minence of the protuberances on the middle lobe of the head. It seems extremely doubtful 
whether all the figures given in the works of foreign authors under the name C. Blumenbachii, 
are of that species. A form referable to C. Blumenbachii (Silurian Researches, pi. 7, fig. 6), 
occurs in the Schoharie grit, and several fine specimens have been obtained by Mr. Gebhard 
of Schoharie. By reference to the table of strata, it will be seen that the fossil described 
holds a much lower position. 
Locality —Lockport, in Niagara shale; also at Rochester and intermediate points. 
4. Bumastis Barriensis (Murchison, Silurian Researches, p. 656, pi. 7 bis, fig. 3, a, b, 
c and d; pi. 14, fig. 7, a and b). “Head round in front; margin raised ; oculine protuberances 
large, surrounded by a depression, on the edge of which, over the eyes, [are] two small ovate 
prominences ; in advance of the eye, and towards the margin, two slight hollows. Eye ap¬ 
proaching to semilunar, apparently smooth. The facial suture traverses the oculine pro¬ 
tuberances, separates the upper portion of them from the eye, and passes under the margin. 
Body with no true longitudinal furrows ; central lobe only just perceptible by a slight depres¬ 
sion in the body only. Ribs 10, those of the lateral lobes terminating in recurved blunt ends. 
Caudal portion round and smooth, without a trace of trilobation. Surface of the whole animal 
covered by extremely thin, apparently imbricated lamella, the edges waved or vermiform, the 
intermediate spaces studded with minute dots.” 
This trilobite is readily recognized by the similarity of the two extremities, which are much 
more rounded than in Isotelus. It is known at the locality as the “ Double-headed Trilobite.” 
Our specimens are usually much flattened, and the oculiform protuberances scarcely elevated. 
Although there is no distinct trilobation of the body, there is usually a strong undulation in 
the ribs at the point between the central and lateral lobes. After the removal of the crusta- 
ceous covering, the body is sometimes seen to be covered with minute punctse. In our spe¬ 
cimens, the length of the body is from one third to two thirds the length of the caudal extre¬ 
mity : this circumstance, with the apparently more slender ribs, at first induced me to consider 
it a distinct species. 
Locality —Lockport, in Niagara shale. The head and caudal portions of this fossil are 
often found at Rochester, and in Wayne county, but I have seen no perfect specimens from 
these localities. 
