Width 



in axis 



in pleurae 



9.38 



13 



10 



13.00 



10 



8 



6.25 



10 



8 



536 DESCRIPTIONS OF NEW TWO TRILOBITES^ 



lian forms agree with the British one in more dimensions than they disagree, 

 as will be seen by a study of the following measurements (in millimetres) : 



Length Width Head Thorax Pygidium 



1. P. (larhiensis .. 17.85 10.2 6.2 long 6.2 long 5.45 long 



2. G. convexicandatus 25.0 14.06 7.8 (?) 8.6 8.6 



3. New Specimen .. 12.5 7.8 3.9 4.7 3.9 



The ratio of length to width is the same in the first and third and nearly 

 so in the second, the measurements of the separate parts showing variation. In 

 the case of the second specimen it is possible that the measurement given lor its 

 head is not correct, because of the damaged state of that part. I am disposed 

 to think that in this fossil the head, thorax, and tail have almost) equal lengths; 

 and also that the variation in the length of the thorax of the third arises as a 

 result of its immaturity. It is in the pygidia that the Australian and British 

 examples differ most, as the following dimensions of the pygidia will show: — 



Seg-ments 

 Length 



1. P. darbiensis 6.25 



2. G. convexicaudatus .... 9 . 40 



3. New specimen 3.90 



It is thus seen that the ratio between length and width of these three fossils 

 varies little and that practically the only differences worthy of consideration 

 from a specific point of view are those which occur in the number of the seg- 

 ments in their pygidial axis and pleurae. No doubt these are fixed and constant 

 differences and are sufficient to separate the two forms. 

 Family PROETIDAE. 



COEDANIA GAHDNERI, n.Sp. (PI. liv., figS. 1-7.) 



Spec. Chars. Head-shield subsemicircular, densely tuberculated, strongly in- 

 flated. Glabella mildly convex, subcylindrical, relatively short, front gently 

 rounded, sides subparallel, separated from the frontal limb by the continuity of 

 the axial furrows, fairly densely covered with tubercles of different sizes. Basal 

 lobes small, circumscribed, and each bearing two prominent tubercles and other 

 smaller ones; neck-furrow shallow, its lateral extensions interrupted by the 

 tuinidity of the fixed cheeks adjacent to the axial furrows, from thence across 

 the free cheeks wide and shallow ; occipital ring moderately strong, convex and 

 gently arched backward; lateral extensions ridged, subprominent and granulated. 

 Frontal limb very wide, convex just in front of the glabella, thence concave to 

 the upturned border, the convex portion thickly covered with several irregular 

 rows of bead-like tubercles, most dense and largest near the antero-lateral angles 

 of the glabella, the tubercles on the concave portion finer; border, along its outer 

 edge, bears a row of moderately distinct pustules. Fixed cheeks tumid, lower 

 than the glabella; on each, between the palpebral lobe and the axial furrow is a 

 row of four tubercles, of which the anterior one is the largest and encroaches 

 upon the furrow, causing it to indent the glabella. Free cheeks strongly in- 

 flated, steep between the eyes at the top and the borders at the bottom, between 

 which they are conspicuously tuberculated; borders abnormally wide, concave be- 

 tween the cheeks and the thickened margins, which concave portions are only 

 finely and sparsely tuberculate; both outer and inner edges of the margins are 

 granulate; the genal angles are produced into stout spines. Eyes small, reni- 

 form, apparently faceted, prominent, separated from the cheeks by a distinct 

 furrow, subdistant from the glabella and, for the gi-eater part, in advance of the 



