22 PALEONTOLOGY. 



Entire surface apparently smooth, excepting fine radiating striee on the 

 . anterior and lateral portions of the cephalic shield, that are scarcely visible 

 witliout the aid of a magnifier. 



Whole length, 1.60 inches; breadth of thorax, 1.07 inches; of cephalic 

 shield (somewhat flattened by pressm^e), about 1.12 inches; length of thorax, 

 0.70 inch; length of pygidium, 0.30 inch; breadth of same, 0.60 inch. 



Of this fine Trilobite, three entire specimens and a part of another were 

 obtained. They are, however, all merely sharply-defined natural casts, 

 formed by the deposition of a crust of arragonite in the original moulds left 

 by the fossil in some kind of a matrix. The specimens were evidently some- 

 what flattened by pressure before or at the time they left their impressions 

 in the rock. This compression has obscm'ed the lateral furrows of the gla- 

 bella; but most of the other characters of the npper side of the fossil are 

 clearly seen, even to the facial sutures, and the faintly-marked radiating 

 strise around the front and lateral, margins of the cheeks. 



The genus Conocephalites (or more properly Conoconjphe, for a strict 

 application of the rules of priority would, I should think, require that the 

 latter name should be adopted for the genus to which they were both 

 applied) is so nearly allied to Olenus that it may not be always easy to dis- 

 tinguish the two types without seeing the hypostoma, and hence it is possi- 

 ble that the form under consideration may be more properly an Olenus. As 

 it has more the regular oval outline of the former, and less pointed and pro- 

 duced pleurae than the latter, while it shows' clearly the fine radiating striae 

 around the anterior and lateral margins of the head, so often seen in Cono- 

 coryphe^ it more probably belongs to that genus. It is worthy of note, how- 

 ever, that all of the specimens seem to be much more depressed or flattened 

 than any of the species yet described of that genus, while only one of them 

 shows any traces of the slender ridge usually seen passing from the ante- 

 rior end of each eye to the front extremity of the glabella; and in this one, 

 the ridge is so faintly marked as to leave doubts whether or not it is 

 natural. 



The slight difi'erences between some of the details of the type speci- 

 men illustrated on our plate, and those figured by Dr. White, are either 

 sexual, or due to accidental causes. The most obvious of these differences 



