GEOLOGICAL SOCIETY OF PENNSYLVANIA. 



263 



NOTICE OF NONDESCRIPT TRILOBITES, FROM THE STATE 

 OF NEW YORK, WITH SOME OBSERVATIONS ON THE 

 GENUS TRIARTHRUS, &c. By Richard Harlan, M. D. 



Having recently enjoyed an opportunity of inspect- 

 ing several new species of Trilobites, in the cabinet of the 

 Lyceum of Natural History of New York, which were 

 obtained from Utica in that state, and which were sup- 

 posed, at first view, to belong to the new geuus Triarthrus, 

 proposed by Dr Green^ in order to include a peculiar 

 species ; I have been enabled to correct the erroneous 

 impression on which this genus is constructed, and which 

 were, perhaps^ unavoidable from the imperfection of the 

 fossil specimens of this kind which have hitherto come 

 under the observations of authors. Among the numerous 

 specimens above referred to, occurs one complete im- 

 pression of the whole animal, from which it is clearly 

 demonstrated that the only portion of this animal previ- 

 ously discovered, consisted of the buckler and not of the 

 body. The latter having been composed of softer materials 

 has, in most instances, been obliterated; consequently the 

 characters which were supposed to distinguish a peculiar 

 genus, under the name of Triarthrus (vide Green's Mon- 

 ograph of N. A. Trilobites, p. 86), having been drawn 

 from the head or buckler of an individual under the erro- 

 neous impression that it constituted its abdomen and tail^ 

 cannot by any means be brought to practicable applica- 

 tion, and the genus Triarthrus becomes obsolete. 



But this is the less to be regretted in the present in- 

 stance, inasmuch as by modifying and contracting the 

 characters on which the genus Paradoxides of Brong- 

 riiart orEntomostracites of Wahlenberg is constructed, it 



