346 



Notice of a new Trilobite. 



Art. XL — Notice of a new Trilobite, Ceraurus crosotus ; by 

 John Locke, M. D., Professor of Chemistry and Pharmacy in 

 the Medical College of Ohio. 



Messrs. Silliman — I enclose to you 

 a drawing of a new species of trilobite, 

 evidently of the genus Ceraurus of 

 Green. It is one of the smallest, and 

 at the same time one of the most ele- 

 gant of this family of extinct crusta- 

 ceans ; this drawing being magnified 

 three times in linear dimensions. Frag- 

 ments of this species have been re- 

 peatedly found in the rocks of this 

 vicinity, especially the fringed mar- 

 gin of the shield ; but it was not until last summer that I pro- 

 cured a specimen so nearly entire as to determine its generic 

 relations. When Dr. Green established the genus of Ceraurus, 

 it consisted of only one species, the Pleurexanthemus. But 

 now that other species very closely allied to that are found, 

 the justness of his discrimination is very apparent. I have 

 named this new species crosotus, from the Greek word, signi- 

 fying fringed. Dr. Green's description of his species — " Cly- 

 peo, postice arcuato, angulo externo in mucronem valde pro- 

 ducto, occulis minimis remotis, post abdomine in spinam arcua- 

 tam utrinque extenso," — applies quite well to the crosotus ; 

 but this last differs from the former in having the shield pectinate 

 or fringed anteriorly. The spines of the shield and of the several 

 ribs are more nearly straight. Besides the spines terminating the 

 ribs, there are six slender teeth, similar to those of the anterior 

 fringe, attached, not to ribs, but to the terminal margin of the 

 tail, four of them between the two last costal spines, at a, and 

 the other two outside or anterior to the same, at b. Each of the 

 costal arches is marked by ttvo tubercles or " pimples," (one in 

 the other species,) one on its middle, and the other at the com- 

 mencement of the free spine in which each costal arch termi- 

 nates. These tubercles form four rows or lines down the body, 

 two on each lateral lobe, the inner one being in the direction of 

 the distant eyes. 



Cincinnati, Ohio, Dec. 9th, 1842. 



