BY R. ETHERIDGE, JUN., AND JOHN MITCHELL. 171 



sutures straight. Pygidmm subtriaiigular, small, anterior margin 

 straight and twice as long as axial length of the pygidium ; axis 

 prominent, reaching to the posterior margin, subtruncate, divided 

 into three segments ; pleurse composed of two coalesced segments, 

 moderately inflated, margin narrow and thickened, no striation 

 visible. 



Obs. — Since the description of this species by one of us, a large 

 addition has been made to our material, which enables us to give 

 fuller specific details. One important feature possessed by some 

 of the specimens, and not present on the original example, is the 

 presence of a large dorsal spine. Different specimens of the head 

 shield show variations in the width of the limb, size of the eye 

 lobe, distinctness and presence of glabellar furrows, and apparent 

 shape of the eye ; but all these differences we conclude to be 

 insufficient to establish more than one species. Most of the 

 variations may arise from compression, and the oval impression 

 left in some cases where the eye has been broken off are treated 

 as accidental. As we are unable to observe any marked differences 

 between the cephalic shields of those specimens with dorsal spines, 

 and those without that appendage, it has struck us that this 

 feature may be no more than a sexual characteristic. 



C. howningeyisis is closely allied to G. Burmeisteri, Barr.,"^ but 

 is longer in proportion to its wddth, and seems to have a much 

 more attenuated pygidium and thoracic axis. In addition there 

 is the possibility of glabellar furrows. In dealing with small and 

 often ill-preserved remains such as these, it is sometimes difficult 

 to be certain what is pure structure or what may be the result of 

 pressure. If the apparent glabellar grooves sometimes observable 

 in C. bowningensis, such as are shown in PL vi. fig. 3/-g, be truly 

 of that nature, they would tend to place the species near the 

 genus PhcBtonides, Angelin.f The ovate character of the entire 

 test is one in which notably the present species and also our C. 

 Horani, agree with several American s[)ecies of the Hamilton 

 Group. 



* Syst. Sil. Boheiiie, 1852, 1. p. 484, t. 18, f. 61-71. 

 t See Hall, Pal. New York, 1888, vii. p. xlv. 



