TJw Trilobites of the Bok'keveld Bech. 209 



PHACOPS IMPRESSUS, sp. nov. 



Plate XXV., figs. 1, 2. 

 18oG. Phacopfi {Cri/pJueiis) caffcr, Salter (pars)'?, Trans. Cleol. 

 Soc, ser. 2, vol. vii., p. 219, pi. xxv., fig. 18 only. 



This form is represented by several nearly complete specimens, 

 but they are so much crushed and distorted that it is impossible to 

 determine accurately the characters of the head. 



The outline of the head appears to have been nearly semicii'culai' 

 and the genal angles were probably angular, but not produced into 

 spines. The glabella is narrow, forming considerably less than half 

 the total width, and it is nearly parallel-sided ; the glabellar furrows 

 are all deeply impressed, but the second is very short and does not 

 reach the axial furrows, so that the first and second glabellar lobes 

 are not completely separated exteriorly. Eyes large and prominent. 



Thorax somewhat depressed. The axis forms about one-third of 

 the width ; the rings of the axis are strongly nodular at their 

 extremities. Pleurae deeply grooved, and, so far as visible, obliquely 

 truncate, the posterior ones being probably produced into short 

 points. 



Tail triangular, slightly arched. Axis narrow, not prominent, 

 conical, terminating in a point which does not quite reach the 

 posterior margin ; it bears eight or nine rings, of which the first four 

 are quite distinct and the last three tend to become obsolete. Lateral 

 lobes but little inclined, with five deep and narrow furrows sepa- 

 rating the wide flat ribs — a very short sixth furrow is visible on the 

 best preserved specimens —each of the ribs is divided by a fainter 

 furrow ; the ribs and furrows do not reach the margin. The margin 

 is produced into a series of very short points, but tlie inunber of 

 these is uncertain. 



licmarks. — This appears to be tlie form referred to Ijy Salter under 

 the heading " Phacops, sp. No. 3," and, chiefly from the characters 

 of the tail, 1 am inclined to think that the specimen which he 

 figures in pi. xxv., fig. 18, as Pliacop.'i cdjf'rr, really belongs to this 

 species. 



Affinities. — In spite of the points borne by the margin of the tail, 

 PhacopH inipirssu-s is not a typical Cri/pJueiis, and it is probable that, 

 together with the preceding species, it should constitute a new sub- 

 genus ; but in the absence of more perfect material it would be 

 difficult to specify the subgeneric characters. 



