RAYMOND AND BARTON: AMERICAN SPECIES OF CERAURUS. 529 



which have been referred to this species, and the Geological Survey 

 of Canada, through the courtesy of Director Brock, has loaned a con- 

 siderable number of specimens. 



The type of Ceraurus pleurexanthemus is well known from the plaster 

 casts distributed by Green, and the original specimen was refigured by 

 Hall. The cast shows a very poorly preserved trilobite, about 25 mm. 

 long, with the greater part of both cephalon and pygidium buried in 

 the matrix. The cephalon shows a pair of narrow flaring genal spines, 

 and small, prominent eyes, which are nearer to the glabella than to the 

 posterior margin of the cephalon. The greater part of the glabella and 

 all of the anterior margin of the cephalon are concealed. On the fixed 

 cheeks, just inside of, and behind the eye, are two small, sharp tubercles 

 which seem to be present in all species of Ceraurus. The thorax 

 shows 11 segments; the axial lobe is convex, prominent, a little less 

 than one third the total width. The pleural lobes are flat to the ful- 

 crum, where there is a line of prominent nodes. The part of each 

 pleuron within the fulcrum is divided by a diagonal furrow into two 

 triangular nodes. The pygidium is mostly concealed, but shows one 

 of the long spines which characterize the genus. 



A study of the numerous specimens of Ceraurus at hand has con- 

 vinced us that the position of the eye is an important and constant 

 character, and in this respect Green's type agrees with the specimens 

 found at Trenton Falls, N. Y. The other characters, in so far as the 

 cast shows them, are also in accord with the specimens from that 

 locality. Trenton Falls is only about fifteen miles from Newport, 

 which is given as the locality from which the original specimen was 

 derived, but the strata there are somewhat higher in the Trenton than 

 are those at Newport. However, it is not at all impossible that the 

 original specimen may have come from Trenton Falls, as that place 

 had been known as a locality for trilobites long before 1832. In any 

 case, specimens from Trenton Falls may be taken as typical of the 

 species, and the description here given is derived from specimens found 

 there. 



Description. — Body, disregarding spines, obovate, with flaring 

 spines at the genal angles and on the pygidium. Axial lobe about 

 one third the total width, convex, and tapering but slightly. 



Cephalon broad, roughly semicircular in outline, about .4 as long 

 as broad. Glabella very convex, expanding forward, and reaching 

 the frontal margin. The expansion is slight, averaging about 1 mm. 

 in 7. The front of the glabella is nearly square, being but slightly 

 curved. There are three pairs of glabellar furrows ; the first two pairs 



