44 NEW YORK STATE MUSEUM 



line rimiiij; the jHistorior inar^Mii. but the head not separated 

 at .the sutui-e: jrhihella lobed." Hairaude protested strongly 

 and repeatedly against the subdivision, principally <m the follow- 

 ing grounds: the eye line is not a suture but only a single 

 nervure, as is visible in many other Trilobites; and the fiv€ seg- 

 mented thorax is of no account because of the metamorphosis 

 undergone by Trinueleus. Nicholson and Eiheridge, after the 

 examination of a great number of specimens, fully concur with 

 Barrande as to the unimportance of the number of the segments 

 and the presence of the eye line, and therefore conclude, that 

 Tretaspis as proposed by McCoy or Salter can not stand, but at * 

 the same time hold, that it may be advantageous to retain the 

 term for that section of the genus Trinueleus which possesses a 

 lobed glal»ella. 



Beecher has shown (Am. jour. sci. 1895. 49:307) that Trin- * 

 uclens concent ricus, in its adolescent stage, posseeses 

 the features pointed out by McCoy and Salter as characteristic 

 of. the genus Tretaspis, and on this ground is inclined to reject 

 McCoy's divisions of the genus Trinueleus, as Barrande did. 



The cephala here described as those of Tretaspis clearly agree 

 with the cephala of the young individuals of Trinueleus 

 concentricu.e, figured in Beecher « excellent paper, in pos- 

 sessing the so called eye-lines and eye- tubercles. While, how- 

 ever, that investigator states that these features disappear when 

 a width of 5 mm is attained, they are still distinctly preserved 

 in the specimen figured on pi. 3, fig. IS, which has attained a . 

 width of 13 mm. that is, nearly the average size of the specimens • 

 of T r i n u c 1 e u s c an centric us, and shows mature devel- 

 opment of the border. Furtheniiore, the specimens from Ryse- 

 dorph hill have the pitting which is so distinct in the stages 

 figurcMi by Beecher, and which also, as a very fine pitting, is 

 still present on the mature Trinueleus concentricus, 

 accentuated into a coarse reticulation. Also in the relatively 

 small size of the glabella and the apparent absence of genal 

 spines these sj)ecimens retain adolescent features. On the other 

 hand they fail to show any indications of the triangular areas 



