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REVIEWS — CRANIA BRITANNICA. 



discovered by Mr. Blackwell, a small spine of a somewliat ligliter 

 color than tlie otlier portions of the shell, is seen to pass into these. 

 The faculty of imbrication seems, however, to be incompatible with 

 the existence of hard spines on the under sides of the pleurse ; more 

 especially as no trace of a short longitudinal groove or other depression 

 occurs on their upper surfaces, against which, during imbrication, the 

 spines must have been pressed. As the peculiar pit-marks here 

 described, do not appear to have been previously noticed on any 

 example of a trilobite, we are induced to call attention to them in the 

 hope that further light may be thrown upon their occurrence by the 

 observations of other palaeontologists. 



"We have arranged in the following table the five Canadian species 

 of Asaphus discovered up to this time. Only two forms, it will be 

 observed, occupy the same division ; and, in these, the opposite 

 characters of the pleurae are alone sufficient to establish a distinction 

 of species. 



The horned species of the genus Asaphus fall naturally into two 

 groups : in one of which, the horns are broad and flat ; and, in the 

 other, thin and cylindrical. The recognised Canadian examples 

 belong to the latter type — a type apparently unknown amongst the 

 European species. Hall's Asaphus Barrandi, on the other hand, is an 

 American example of the first type. 



REVIEWS. 



Crania Bbitaknica ; Delineations and descriptions of the sJadls of 

 the early inhabitants of the British Islands, togetJier with notices of 

 their other remains. By Joseph Baenaiid Davis, M. E. C. S. E., 

 and JoHK Thurnam, M. D, Decade III. London : Tfylor & 

 Erancis, 1858. 

 Another fasiculus of this important contribution to the physical 



ethnology of the British Islands, has come to hand ; and amply sua- 



