142 



Contributions to Palceontology. 



ened border which is produced anteriorly, and the 

 posterior extremity extends in a slender spine. Sinus, 

 formed by the eye-tubercle, of medium size. 

 In two specimens, carefully measured, we have the entire 

 length of glabella 0-30 of an inch ; width of glabella at 

 base, 0-29; at apex, 0-18; entire length of head, 0-44; 

 frontal limb, 0-10 of an inch. In another specimen, these 

 measures are respectively 0-25, 0-23, 0-14, 0-38, 0-09. 



This species, in its glabella and frontal limb, somewhat resembles 

 C. eryon (fig. 16), but the proportions are somewhat different : the 

 glabella is narrower at base and much more convex; the frontal 

 limb is not quite so extended, and is more convex ; the facial su- 

 ture continues its vertical direction farther down, leaving a narrower 

 posterior limb of the fixed cheek. 



The heads and cheeks of this species, in the condition represented 

 on the plate, occur in myriads in certain layers at Marine mills : the 

 slabs are covered with these, and remains of two other species which 

 are comparatively rare. This position, according to Dr. Owen, is 

 above the middle of the Sandstone series in the Fourth Trilobite 

 bed. 



The Conocephalites (Lonckocephalus~) chippewaensis of Owen is 

 cited by that author as occurring in the fourth or Marine mills 

 - Trilobite grit ; and before I had critically examined this one, I 

 supposed the smaller specimens to be the same. After having studied 

 numerous specimens without finding evidence of a spine from the 

 occipital ring (that being a conspicuous feature of the C. chippewa- 

 ensis), lam constrained to refer the specimens to some other species. 

 Most of the specimens, moreover, are much larger than the figures 

 of Dr. Owen. 



In some of the slabs from Marine mills there are spines which 

 appear to have belonged to the posterior part of the head of some 

 trilobite, and these may possibly belong to the species of Dr. Owen 

 which I have failed to procure. Some of the species appear to be 

 restricted to a very limited range, and it is quite probable that my 

 specimens are from a different layer than that in which C. chippe- 

 waensis occurs. 



