Contributions to Palaeontology. 



155 



very narrow posterior limb, the extent of which is un- 

 known. Frontal limb extended about two-thirds as 

 long as the glabella, depressed convex on its posterior 

 half ; thence gently curving downwards towards the 

 front, it is marked a little in advance of the middle by 

 a low ridge, on each side of which is an undefined fur- 

 row, leaving the anterior border a little narrower than 

 the posterior convex portion. 



This species differs fron the C. wisconsensis in the less lateral 

 extension of the frontal limb, the narrow subcentral transverse 

 ridge and shallow furrows, and in the proportionally longer glabella. 



PLATE III. 



Fig. 25. The glabella and part of the fixed cheeks, with frontal limb 

 and posterior spine. 



Fig. 26. Profile of same. 



The remarkable spines, which occur in the same association, are 

 represented on Plate II and on Plate vi, figs. 5 & 6. These appear 

 more like cheek-spines than glabellar spines j but it is still impossi- 

 ble to assign to them their true relations, with our present know- 

 ledge of the parts of trilobites occurring in the same association. In 

 some forms or conditions, as fig. 44 of Plate n, we might suppose 

 them to be cephalic spines ; but in the condition of fig. 6, Plate vi, 

 we cannot so readily assign them a place j and this question becomes 

 still more difficult of solution when we find them in the condition 

 of fig. 5, where there is an expansion like a part of the cheek 

 within the curve of the thickened border. These spines do not 

 represent the posterior spines of the cheeks, for they have no 

 groove on the upper side, or evidence of infolding of the crust on 

 the lower side ; but the thickened parts near the base are rounded 

 above, slightly flattened below, and longitudinally striated, with 

 that extremity sharply truncated as if by a suture. In the speci- 

 mens fig. 5, there is, on what may be the posterior side, a narrow 

 thickened border not unlike a cheek-border, with the impression of 

 a thin expanded crust resembling a cheek-shield irregularly broken 

 off along the inner margin. 



We might suggest that the spine, like fig. 5, proceeded from the 

 middle or anterior part of the movable cheek, near the facial suture, 



