cc INFERIOR OOLITE AMMONITES. 



coincide with or produce the acme of a genetic series. For another factor comes 

 in here — individual bulk. The period of attainment of the largest individual growth 

 by a particular species of a genetic line must be regarded as the genetic acme ; and 

 although there is a certain relation between the acme of ornament-elaboration 

 and the acme of bulk-development, yet they do not coincide. Rather the acme of 

 ornament is reached before the acme of bulk — sometimes shortly, sometimes at a 

 longer period, before — as if a certain economy in reduction of ornament were 

 necessary and favourable to the attainment of greatest individual growth. 



To take examples : Vermiceras Gonybearii compared to Goroniceras, 8tepheoceras 

 compared to Goeloceras Blagdeni, Sonninia dominans compared to 8. crassispinata, 

 are all cases where the acme of size comes shortly after the acme of ornament. In 

 Parkinsonia dorsetensis (Wright), the giant of the Inferior Oolite, the acme of size is 

 long after the acme of ornament — for that must be reckoned as Goeloceras- 

 Blagdeni-eqmYdleTit in this series — a stage from which Park, dorsetensis has 

 travelled far : it only shows the morphic representation thereof in its brephic 

 whorls. In the Lytocerata, too, the growth-acme is long after the ornament-acme ; 

 for Lytoceras fimbriatum is about in the acme of ornament in this series; but it is a 

 small species beside such giants as Lytoc. sigaloen, L. Wrighti, L. confusum, which 

 have left the ornament-acme so far behind that they only show, at a very youthful 

 period, traces of a stage somewhat analogous to that of L. fimbriatum. 



To consider the various characters and their morphogeny : In whorl-shape, 

 inflation is anagenetic, and contraction is catagenetic. In suture-line, the greater 

 elaboration and complication is anagenetic, the simplification is catagenetic. When 

 suture-lines do not increase their complexity more than in proportion to the whorl- 

 increase, but become more approximate — the individual becoming more densisept 

 and less latisept — that must be regarded as a beginning of catagenesis. 



In test-ornament, elaboration is anagenetic, and simplification is catagenetic. 

 The transverse ornament may show the following successive stages of morphogeny : 

 in anagenesis, striation, subcostation, costation, unituberculation, bitubercula- 

 tion, multituberculation ; and, in catagenesis, the same stages in reverse order till 

 all ornament is again lost, and smoothness is returned to. Or, after a period of 

 decline, renewed elaboration may take place ; thus a species which shows in its 

 ontogeny catagenesis from tuberculate to subcostate may elaborate afresh ana- 

 genetic stages from subcostate to tuberculate : Sonninia renovata is a notable 

 example. 



Perhaps it would be correct to regard the tuberculate stage as due to the 

 development of longitudinal ornament across the costate transverse ornament, so 

 breaking up the costse into a row of tubercles in the line of intersection, which 

 often is an angular portion of the whorl area. 



Longitudinal ornament is most frequently developed on the periphery where 



