83 



lobe of the abdomen is much broader than the lateral 

 lobes, and has 13 distinct, double articulations. The 

 side lobes are curved, and each costal arch is flatten- 

 ed anteriorly near their lower extremities, no doubt 

 for the purpose of enabling the animal to roll itself 

 into a ball. The tail is tapering, and is composed of 

 ten articulations. The crustaceous covering is here 

 more thickly deposited than on any other part. The 

 entire shell seems to have been covered with minute 

 elevated dots; these are beautifully distinct on the 

 buckler and on the tail. Whole length of the speci- 

 men described, not quite two inches. 



The other specimen of this species in the cabinet 

 of the Albany Institute, is a large caudal end, three 

 inches arid a half long, entirely perfect. Both of 

 these fossils were brought from Williamsville, Nia- 

 gara county, New York. They occur in a dark shelly 

 limestone, filled with other petrifactions. The cal- 

 careous matter which has mineralized the trilobite, 

 in this instance, as in most others, is of a much darker 

 hue than the surrounding rock. 



GENUS CERAURUS. Green. 



Body, very much depressed, and slightly tapering. 



Buckler, scarcely trilobate; cheeks large, flat, with 

 small remote oculiform tubercles; posterior angle of 

 the buckler spinous. 



Abdomen, with twelve articulations. 



Tail, rounded at the end, but terminating on each 

 side with two slightly curved spines. 



