44 NEW YORK STATE MUSEUM 



line cutting the posterior margin, but the head not separated, 

 at the suture; glabella lobed." Barrande protested strongly 

 and repeatedly against the subdivision, principally on 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 five seg- 

 mented thorax is of no account because of the metamorphosis 

 undergone by Trinucleus. Nicholson and Etheridge, 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 Trinucleus which possesses a 

 lobed glabella. 



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

 ucleus concentricus, in its adolescent stage, possesses 

 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 Trinucleus, as Barrande did. 



The cephala here described as those of Tretaspis clearly agree 

 with the cephala of the young individuals of Trinucleus 

 concentricus, figured in Beecher's excellent paper, in pos- 

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

 ever, that investigatoir 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. 18, which has attained a 

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

 of Trinucleus concentricus 1 , and shows mature devel- 

 opment of the border. Furthermore, the specimens from Kyse- 

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

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

 still present on the mature Trinucleus concentricus, 

 accentuated into a coarse reticulation. Also in the relatively 

 small size of the glabella and the apparent absence of genal 

 spines these specimens retain adolescent features. On the other 

 hand they fail to show any indications of the triangular areas- 



