ACIDASPIS. 13 



The only foreign species which seems to approach it at all closely is Acidaspis 

 lacerata of Barrande, 1 which, indeed, comes so near to it that I was at first in 

 much doubt whether the latter ought not to be regarded as a variety. The chief 

 difference appears to be in the greater width of the head in our species, and the 

 angularity of the border, though it is possible that these points may be accentuated 

 by the defective character of the specimen. The slight groove at the latero- 

 posterior angle is also not seen in Barrande's figure, and would at once be a good 

 distinctive mark were it not possible that the upper layer of the test, which 

 appears to be wanting in our fossil, might not reproduce it. This also might account 

 for the greater rotundity of several of the protuberances in the foreign fossil, but 

 not, I think, for the constrictions and much greater flatness of the glabella; nor 

 does it seem to me that the contour of the posterior part of the cheek could have 

 agreed with it had it been present. The median line of the cheek is much more 

 elevated and longer, the rear spines seem much greater, and the specimen is more 

 than twice the size of Barrande's. I have therefore little hesitation in regarding 

 it as a distinct species, and I have much pleasure in giving it the name of its 

 discoverer, to whose kindness and acuteness I owe so much in my effort to work 

 out the fauna of these beds. 



From most of the other species of Acidaspis it is at once distinguished by the 

 forked spines of the neck-lobe. Of those that possess them A. mira, 2 Barr., has a 

 much more tumid and sloping glabella, and a more squared cheek, the angularity 

 noticed in our fossil being present, but much more to the rear. A. Prevosti? 

 Barr., has no other large tubercles or spines on the glabella, and the cheeks are 

 altogether deeper and rounder. In A. Dufrenoi/i, 4, Barr., the cephalic shield is 

 much more elongate and elliptic. A. Venieuili, 5 Barr., and A. vesiculosa, 6 Beyr., 

 have margins swollen at the sides, so as to give quite a different contour to the head. 



2. Acidaspis pilata, Whidbome. PI. I, fig. 18. 



1889. Acidaspis Htjghesii, 7 Whidb. Geol. Mag., dec. 3, vol. vi, p. 29. 



Description. — Pygidium small, flat, semicircular. Axis broad, last segment 

 forming an ovoid, shallow depresssion filled with two small spherical knobs nearly 



1 1852, Barr., ' Syst. Sil.,' vol. i, p. 746, pi. xxxix, figs. 18, 19, Et. F. 



2 Ibid., p. 735, pi. xxxix, figs. 1—11, Et. E. 3 Ibid., p. 739, pi. xxxix, figs. 33—41, Et, E. 

 4 Ibid., p. 741, pi. xxxviii, figs. 25, 26, Et. E. 5 Ibid., p. 710, pi. xxxviii, figs. 1—9, Et. E. 



6 Ibid., p. 715, pi. xxxviii, figs. 13—21, Et. F. 



7 Mr. Marr points out that Salter has catalogued, without description, a widespread Lower- 

 Silurian Trilobite under this name. In order, therefore, to avoid confusion, I have renamed the 

 Devonian species, although a merely catalogued name has no rightful validity. 



