F. R. Cowper Reed — On Phacops [Chasmops) Marri. 245 



Thoracic axis about one-fifth the width of thorax ; of uniform 

 width ; axial furrows deep. 



Pleuree flattened, with deep oblique furrows ; fulcrum conspicuous, 

 situated at i length of pleura from axial furrow. 



Pleura horizontal and at right angles to axis as far as fulcrum ; 

 then bend back at 30° — 40° to previous direction and curve slightly 

 downwards. 



Extremities of pleurae blunt, rounded, flattened. 



Crust of thorax slightly granular with few tubercles. 



The form above described does not exactly agree with Salter's 

 Ch. macroura (Mon. Brit. Tril. p. 37), but resembles it in the 

 general shape and tubercular character of the head, in the cheek 

 spines, and the course of the facial suture ; but the lobes of the 

 head, the size of the eye, and the cephalic border show important 

 differences. 



With Ch. conophthahmis, as described by Salter (loc. cit. p. 40), 

 it has the transversely overhanging frontal lobe in common ; but 

 there are considerable points of dissimilarity in the length of the 

 genal spines, the tuberculate condition of the head, the size of 

 the eyes, the presence of the middle and basal lobes of the glabella, 

 and the non-continuity of the neck-furrow with the marginal furrow. 



The absence of any description by Salter of the thoracic rings of 

 these species, and the fact that the tail of our specimen is wanting, 

 prevent us making a more complete comparison ; but so far as the 

 comparison goes we see that our form cannot be said to agree with, 

 either of Salter's species. On turning to Schmidt's Memoir on the 

 Silurian Trilobites of the East Baltic provinces we find there are 

 three species with which it has several features in common. In the 

 first place a comparison may be made with Phacops (s.g. Chasmops) 

 Eichwaldi (Schmidt) {loc. cit. p. 117). The figui'es of this form 

 given by Schmidt (taf. v. f. 8 a. h. c. 9) do not bear much resem- 

 blance to our Coniston Limestone specimen, but in the description of 

 the species the characters, shape, and size of the frontal lobe of the 

 glabella are similar, as are also the shape of the first side lobe (in 

 size it seems rather shorter), the cheek margin, and the length, 

 shape, and position of the genal spines. But there are considerable 

 differences in the parabolic shape of the head-shield (which in our 

 specimen is only due to crushing as has been pointed out), the finely 

 granular, non-tuberculate or smooth surface, the total absence of the 

 second side lobe, the more marked chai'acter of the third side lobe, 

 the smallness of the eyes, the swelling out and subsequent tapering 

 of the thoracic axis, and the scarcely perceptible fulcrum of the 

 pleuree. 



Schmidt thinks that his Ph. Eichwaldi is very similar to or even 

 identical with Salter's Ph. (Ch.) macroura. 



Another species — Ph. maxima (Schmidt) (loc. cit. p. 112) — agrees 

 in the shape of the head-shield, the character of the genal spines, 

 and the size, shape, and extent of the first side lobe ; but it differs 

 by having only fine granulations and no tubercles, by the marginal 

 furrow uniting with the neck-furrow, by the second and third side 



