302 i»ALiEONTOLOGY OF NEW-YOEK. 



TRILOBITES OF THE NIAGARA GROUP. 



The following species of trilobites occur in the Niagara group. Several of them are abundant, 

 being found, either as fragments or otherwise, in many localities ; while others are rare, and 

 but occasionally met with in the more perfect exposures of the rock, or in recent extensive 

 excavations. 



669. 1. BUMASTIS BARRIENSIS. 



Pl. LXVI. Fig. 1 - 15. 



JBumastis barriensis. Muhchison, Sil. System, 1839, pag. 656, pl. 7 bis, fig. 3 a, b, c, d j and 



pl. 14, fig. 3 a, b. 

 JllcBuus (^Bumastis) barriensis. Buemeister, 1843, p. 120; Idem, Ray. Soc. translation, p. 103. 

 Bumastis barriensis. Geol. Rep. 4lh Dist. N. York, 1843, p. 102 ; Tables of organic remains 



(same volume), no. 19, fig. 3. 



General form elongate elliptical, the two extremities nearly equal ; head prominent, rounded 

 in front ; eyes large, semilunar or subreniform, situated near the margin ; body composed of 

 ten articulations, having the middle lobe much wider than the lateral lobe, the longitudinal 

 furrow being indicated by a simple bend in the articulations ; extremities of the articulations 

 somewhat obliquely truncated ; caudal extremity semielliptical (or spheroidally triangular?), 

 without any trace of trilobation, strongly articulated to the body by the middle of the anterior 

 side ; crust extremely thin, except on the margins of the caudal shield ; surface lamellose 

 granulate or lamellose punctate, sometimes only lamellose near the margins. 



I have retained this species under the Genus Bumastis, though the difference between it 

 and Ill^nus is not of vital importance. Considerable variety of aspect is presented in our 

 specimens, and the variable proportion of parts at first induced me to regard it as a species 

 distinct from the fossil described by Murchison. A comparison of a larger number of specimens, 

 however, has satisfied me that there is but a single species, and that it is identical with the one 

 described in the Silurian System. 



The body seems to have been somewhat loosely articulated, and to have admitted of con- 

 siderable contraction and extension. In one specimen, having a length of more than two and 

 a half inches, the body occupies only half an inch ; while in another specimen more than an 

 inch shorter than this one, the body is almost as long. In another specimen of three and a 

 half inches in length, the body is twice as long as in the specimen first named. All these varia- 

 tions take place from the great extension or close contraction of the articulations of the body. 

 The surface marking is likewise subject to considerable variation, but the differences in this 

 respect are not found to be in any manner coincident with the changes in proportions of the 

 body. 



