256 



THE GEOLOGIST. 



splendid collection at Strasburg, formed by Prof. Voltz, he 

 was not aware of any principles by which they could be 

 separated into groups, and the differences of specific form be 

 accurately determined. Mr. Phillips proceeded to describe 

 the general structure of Belemnites as consisting of a cylin- 

 drical hollow sheath, with a radiating fibrous structure, the 

 hollow, or alveolus, conical and slightly curved. He men- 

 tioned that the bilaterality of belemnites was generally 

 overlooked ; the sides, front and back, being figured indis- 

 criminately in different works on the subject. So little had 

 been done to determine the value of specific characters in 

 this group, that at present we were quite unable to apply 

 them as evidence in determining the conditions of ancient 

 waters ; and it was desirable to arrange the facts in such a 

 manner as to give them a general value. He had endeavoured 

 to form such a system of measurement, to be applied in the 

 description of the different portions of which belemnites 

 were composed, as should enable him to form conclusions, 

 not merely as to specific differences, but applicable to the 

 mode of life of groups. The form of the belemnitic sheath 

 would be most frequently found to preserve a certain cha- 

 racteristic form^ not specific only, but distributed in groups 

 in various strata. Thus in the cretaceous group of England, 

 Norway, and America, certain forms of belemnite were found 

 with a grove on the anterior side of the base of the sheath, 

 extending as far as the alveolus, and this character was 

 associated with a mucronate point. In many liassic belem- 

 nites, there was no grove on the point, but two lateral groves 

 at the apex. In many oolitic belemnites, there was no 

 grove at the base or on the sides, but a single one commenc- 

 ing at the apex and running down the front. In grouping 

 together these and other facts, and representing them by 

 the term laio^ he wished to be understood as using that ex- 

 pression only in the sense of a laiv of phenomena, and by no 

 means interfered with the idea of a laio of causation. Used 



