THEORY OF RADII U.- \M» MORPHOLOGICAL EQUIVALENT 



\ iayr was the firs! to tematically the uncoiled forma of the 



i 1 groups and distinct species of normal close-coiled Am- 



monitime, 1 thus confirming Pictet'a isolated bu( su observations on 



l . and declared thai Acantboceras, Olcostephanus, and 



Hoplil the radicals of tin- uncoiled tonus previously included under ■ 



numb* D'Orbigny and other authors, and also traced the 



!l nit.-- and Turrilites to an origin in Lytoceras. Ulilig 1 holds views 



ditnilai N mayr, tracing mosl of the Crioceratites to Hoplites, bul con- 



ostephanus, Acanthoceras, and Aspidoceras had also crioceratitic 



Our conclusions, therefore, are in accord with the results of the 



Neumayr, and Dhlig upon the same class of forms. 



AmmonitinsB of the Lias and Oolites in extreme old age, as a rule, lost 



the tubercl nd often the keel, the whorls became smooth, and decn 



ike on a rounded or triangular outline in Bection, according 



to the group in which the Thus, in Plate I.. Fig. -1 and 25 



show th.- changes which took place in tin- old whorl ofCai.raricostatum,a.nd I I 



and •_' the similar effects in the old age of Qui .,/, The whorl in both be- 



led,andlos On Plate V. Fig. 8, 9, maj be seen the old age 



nd on Plate VI. Fig. I. *_'. tli<- similar old n^' metamorphoses 



In these las! the quadragonal whorl of tin- adult became tri- 



»f being rounded by senile degradation as in the firs! instance. 



On PI I, there are illustrations of individuals <>t" Ad. obituum, which 



the results <>i premature old age in this -: 

 I until a late period of growth an- identical, and both Pro 

 . : dt and the author have identified them under this name. 

 Ti,,- • all due to tin- loss of power in the old animal, which 



can no longer maintain its normal rati- of increase in size as it grows. Thus 

 mailer discoidnl whorls ol ( th low keels became rounded, and 



■i ti,.- keeled and channelled Coroniccras became tri- 

 gonal. I e of reduction in Bize, intermediate between 



the q I form and completely degenerate rounded whorl of extreme 



known, ti. bed by the pr 



• in Oxyno 

 withstanding tin- • power, and tin- consequent and will 



m_t i.lac- in the old whorl of many species of Vermiceras, 



•lv with Uhl 



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