Aug.. 1893. PROFESSOR BLAKE ON AMMONITES. 141 



it was to state exactly the opposite. How closely Professor Blake 

 has studied recent literature, to find that the length of the body- 

 chamber is considered of the least value among present-day authorities ! 

 We have not been able to do so ; but we do not wonder at it, because, 

 in our opinion, to consider the length of the body-chamber only is 

 absurd. What is required is the capacity of the body-chamber. In 

 an evolute, divergent-sided Ammonite the length of the body-chamber 

 would be short, but its capacity might be exactly the same as in an 

 evolute, compressed Ammonite with a body-chamber three times the 

 length. The capacity of the body-chamber, in proportion to the 

 whole shell, may become a basis for classification — its mere length 

 never can be. 



The form of the Ammonite is stated to depend on the curvature 

 (p. 25). Alluding to the fact that he published a mathematical paper 

 on the subject, Professor Blake proceeds to explain how to measure 

 the curvature. He gives us three methods. He first " assumes that 

 the rate of curvature of the inner edge is the same as that of the 

 outer." But of what use is this method among Ammonites ? The 

 rate of curvature of the inner edge must always be greater than that 

 of the outer edge which subtends it, otherwise Ammonites would 

 very soon fulfil the Yankee's definition of a point — " the small end of 

 nothing whittled down." Nevertheless, our m.athematician pro- 

 ceeds to use this wonderful method, and finds thereby that there is 

 considerably less curvature in an involute Ammonite than in an open- 

 whorled Cvioceras ! Now if we take his second method and apply it 

 to the very figures he has given us — the curvatures of the involute 

 Ammonite and of the open-whorled Criocems, work out the same 

 within O'oi. 



In the next paragraph we are introduced to the wonderful 

 ^' Atmnonites transmognjicabilis, Blake ; " and the Professor sets himself 

 to contradict what he had stated in the paragraph above. As a result 

 of his measurements he found that an involute Ammonite had a 

 smaller curve than an open-whorled Cvioceras ; here he tells us that 

 " without altering the curvature " — the italics are ours — he can make at 

 will an involute Ammonite or an open-whorled Crioceras by means of 

 some wonderful diagrams (pi. i., figs. 3, 4, 5), When, however, we 

 come to apply to these figures his first method of estimating the 

 curves — the method he himself thought fit to employ for figs, i, 2, 

 pi. i. — we find he has altered the curvature very greatly, for the ratios 

 are fig. 3, 1-53 ; fig. 4, 1*44 ; fig. 5, i'25 ; and " the greater the ratio 

 the less the curvature" (p. 26). 



Now, we confess to little mathematical faculty ourselves. To us 

 a sum is like a joke to the proverbial Scotchman — only to be done 

 weeth deefeculty ; but even our inferior faculty would have suggested 

 that to estimate the curve of an Ammonite-shell it was necessary to 

 consider not only the peripheral, but also the antiperipheral, or inner- 

 marginal curve. There is no difficulty in seeing that the inner- 



