34 ME. E. S. C0BE0ED ON THE TRILOBIXE FAUNA [VLarch I913, 



Cranidiem: General form. — Irregularly pentagonal, with the 

 front angle rounded, the base somewhat three-lobed, and the sides 

 contiguous to it a little irregular. 



General convexity. — In the smaller specimen [1886] (fig. 3) 

 the ratio is 1 : 2'7. 



Size. — Varying from 2*5 to 20 millimetres in length. 



Dimensions of three specimens in millimetres. 



Number of specimen [1407] 



[1411] J [1886] 



Length, omitting the spine 



19 

 28 

 23 

 22 



ca. 15 6 



ca. 22 : 8-5 

 ca. 19 '; 7-5 

 ca. 17 6"5 



Width across eye-lobes 





A comparison of these three sets of measurements proves that 

 the crushed specimen [1407] has given way vertically, and has not 

 been materially widened by pressure, except possibly at the anterior 

 angles. 



Glabella. — Strongly convex; highest at about the middle of 

 its length, widest at a point somewhat in advance of this ; with 

 sides nearly straight posteriorly ; apex well rounded and reaching 

 the front marginal fold ; without actual furrows, but their positions 

 are indicated by the absence of rugosities on the exterior (see 

 p. 35). 



Occipital furrow. — Wide and rather deep. 



Occipital ring. — About an eighth of the length of the shield, 

 exclusive of the spine ; armed with a rather short spine rising from 

 the upper surface of the ring, and directed upwards and backwards. 

 The specimen [1882] (PI. Ill, fig. 2), from which the spine came 

 away during development, shows the impression of the doublure or 

 nether side of the ring. 



Axial furrow. — Very strongly marked in the internal casts 

 [1407, 1886] (PI. Ill, figs. 1 & 3) ; but narrow and only slightly 

 impressed on the exterior [1411] (fig. 5). 



Fixed cheek. — Trapezoidal; about half as wide as the glabella 

 at a point opposite to the eye-lobe ; highest close to the axial 

 furrow ; moderately convex towards the e} T e-lobe, strongly convex 

 both forwards and backwards. 



Ocular ridge. — Absent. 



Eye-lobe. — Situated so that the anterior end is opposite the 

 middle of the length of the cranidium ; about a quarter as long as 

 the glabella ; with a depressed crescentic area and a decidedly raised 

 and rounded margin (PI. Ill, fig. 5). 



Postero-lateral border. — Consisting of a strong marginal 

 fold and a wide groove, both of which lose force towards the facial 

 suture ; strongly convex downwards, almost geniculate, from a 



