114 Forty-fourth Report on the State Museum, 



of the Geological and Natural History Survey of Canada. This 

 specimen is a portion of the cephalon and a pygidium of Terataspis 

 grandis, lying in juxtaposition on the same block, there being no 

 doubt of their having belonged to the same animal. From this speci- 

 men it was possible to establish the relative proportions of cephalon 

 and pygidium in this species, and from the data furnished by all the 

 material under study, with careful comparative measurements of entire 

 specimens of Lichas in the collections of the State Museum, and of 

 figures of such specimens as have been given by Angelin, Bakrande 

 and Schmidt, the accompanying reproduction of the original size of 

 the animal has been drawn, its base being the largest and most com- 

 plete cephalon figured in the work cited (pi. xvii, fig. 1 ; xviii, figs. 1, 2). 



This restoration gives to the proprietor of this cephalon a length of > 

 nearly 20 inches. The figure does not however do full justice to 

 the proportions of the animal. In the cephalon which has served 

 as a base for the restoration the great ovoid central lobe of the 

 glabella has a length of 2J inches. Mr. Billings speaks of a 

 specimen of Lichas superbus in which the length of this lobe was fully 

 3 inches. If the increase in size of this part was accompanied by 

 the same relative increase in the size of the entire animal (and there 

 is no good reason for assuming the contrary), such a fragment would 

 represent an individual fully 24 inches in length, a size unsur- 

 passed and unequaled by any other known trilobite. 



With his extravagant armor of defense and aggression, Terataspis 

 grandis must have been easy lord of his invertebrate domain and no 

 very palatable morsel for the heavily plated fishes of his day. 



In the genera Phacops and Proetus great size was never attained. 

 The earlier forms of both of these genera were of inconspicuous pro- 

 portions and their maximum size was attained in the middle Devonian. 

 An entire Phacops rana is figured in the Palaeontology of New York, 

 Volume yil, which has a length of 4 inches, and cephala in the 

 Museum collection indicate an original length of 5 inches, perhaps 

 the greatest size which has been observed in this genus. Proetus has 

 a still smaller habit, that is, its maximum size is never so great, and, 

 probably, the largest example of the genus recorded is represented 

 by a cephalon of Proetus macrocephalus from the Hamilton group, 

 which belonged to an individual fully 3| inches in length. 



