320 ME. s. s. srcKMAJ^ ON [vol. Ixxiii, 



on to describe, not this specimen, but his large example of 8 inches 

 in diameter as in the C. C. paper, though occasionally referring to 

 the figures of pi, xxiii — the 160 (166) mm. or 64-inch specimen. 



In regard to the figs, in pi. xxxii he s&js ' Small specimen 

 PI. xxxii, figs. 5-8 [5, 6], Diameter 80 mm.,' and so on — the 

 proportions wliich he gives work out as 80, 19, 19, 62, though 

 the fig. gives 83, 22, 18, 61. It might be urged from this that 

 Wright must have measured from the actual specimen, and not 

 from the C. C. figs. But, in view of what comes out in other 

 cases, this fact of the measurement hardly carries the weight that 

 it might. Suppose, however, that this be accepted — -that this 

 specimen was a small one — it leads to curious difficulties. The 

 specimen certainly does not show what Wright figured it for in the 

 Monograph — 'that j3Egoceras Bircliii maintained its original form 

 and structure through the various phases of its life ' — Explanation 

 of pi. xxxii. For the shell shows that if small it could not jDOssibly 

 be a young hirclii. It has the proportions of an adult. To be a 

 young hirchi it would have to show no more than 6 turns at this 

 diameter, only about 23 spines on the outer row of the outer whorl, 

 and proportions 83, 27, — , 53. Also it should show a smooth 

 stage up to half an inch in diameter, as Wright says in his C. C. 

 paper — his figure shows only a smooth stage up to about a fifth 

 of an inch in diameter, which would be correct for a shell reduced 

 to less than half. 



If, however, this be not a 3''0ung hirclii, but is still figured of 

 natural size, then it must be regarded as a development of lircln 

 which has taken on the characters of adult hirchi at a smaller 

 size — an instance of acceleration or tachygenesis. That it shows 

 so exactly the number of turns, the width of umbilicus, the 

 narrow whorl of an adult, that it has kept exactl}^ the number of 

 tubercles — 33 — on outer row of last whorl, that it shows no change 

 in character of tubercles, no further differentiation between outer 

 and inner rows of tubercles, no sign of degeneration, and no change 

 except a degree of whorl-compression which might be found to a 

 great extent in a specimen of 203 mm. as compared with one of 

 160 mm., strains credulity too greatly. That a small shell, being 

 a morphic representative of an adult, and necessarily as a develop- 

 ment of it separated from that adult by a very great number of 

 generations, should yet be almost a photographic likeness of the 

 adult, is a degree of similarity in morphic representation which 

 seems far too exact. 



I think, therefore, that Wright's C. C. fig. of Ammonites hircJiii 

 which he reproduced in his Monograph as a small shell, is really 

 his large 8-inch example figured less than half natural size, that 

 it is only understandable on that basis, and that therefore it is 

 from Lyme Regis and not from Bredon. At any rate the 8-inch 

 hirclii which Wright described in his C. C. paper ought to be 

 still in existence, and Curators would be well advised to look out 

 for it. 



