374 New Species of Trilobites. 



Width at front margin 5| lines. 



Between posterior angles 7 " 



Length of the oblique straight lateral margins 

 which are produced by the truncation of 

 the extremities 1\ " 



Total length 14 " 



The obtusely pointed angles which form the lateral extremities 

 of the head are as already stated broken off but from the detached 

 head of another specimen it would appear that the distance bet- 

 ween the angle and the eye is not quite so great as between the 

 eye and the dorsal furrow. 



It is difficult to give a clear expression of the form of a rolled 

 up specimen of a small trilobite by wood engraving and the fig- 

 ures above given do not convey so clear an idea of the form as 

 could be desired. 



This species is allied to Ulaenus ovatus (Conrad) but differs 

 therefrom in the following particulars. Conrad says that his 

 species has the eyes " placed on a line with the angle in the mid- 

 dle of the side lobes " meaning a line drawn along the bend of 

 the pleurae ; in ours they are outside of that line ; he also says 

 the middle lobe or axis of the pygidium is " convex, rounded and 

 well defined at the extremity " but in this species it is so obscurely 

 defined as to be barely traceable. We have one nearly perfect 

 specimen of I ovatus and in its characters it agrees very well with 

 Conrad's description ; it has ten articulations in the thorax, the 

 bend is at full one half the length of the pleurae ; the axis of the 

 pygidium is not only distinct but even abruptly elevated behind; 

 the eyes are totally destroyed in the specimen but their position 

 seems to be that mentioned by Conrad. 



In the Palaeontology of New-York, Vol. 1, plate 67 two spe- 

 cies are figured under the name of I. ovatus. One of these has 

 eight segments in the thorax but Professor Hall says " it has a 

 strong thick spine at the posterior angle of the cephalic shield." 

 I do not think therefore that it can be identical with ours. The 

 other specimen figured has nine segments in the thorax, and the 

 eye outside of the line of the bend of the pleurae but conical and 

 strongly projecting ; it also differs too much from ours to be 

 regarded as the same. 



Dedicated to T. A. Conrad the first Palaeontologist of the New 

 York Survey. 



Locality and formation. At the falls of La petite Chaudiere, 

 Township of Hull, Black River Limestone. 



