CATAGENESIS. 75 



gibbous ; * that is, after the quadragonal whorl had appeared in the development 

 of the same individual. 



"We have also shown that in every series similar changes took place in the 

 geratologous species, and were accompanied by a correlative series of retrogres- 

 sive pathological changes in the keel, channels, pilas, tubercles, and sutures. The 

 convergence of the sides is, therefore, a retrogressive character when it occurs 

 after the gibbous or quadragonal whorl has appeared either in the evolution of 

 the series or in the development of the individual. In Psiloceras a slight con- 

 vergence of the sides of the whorls was present, and was a primitive character 

 of the helmet-shaped whorl, and this occurred also in Am. miserabile, and in the 

 nealogic stages of other forms of the Levis Stock. Such characters in the indi- 

 viduals of radical species occur before the quadragonal whorl is developed, and 

 in connection with primitive radical characteristics and forms which will not be 

 confounded with geratologous characteristics and forms by any close observer, if 

 he have sufficient materials for study. 



There is a true senile degeneration in the old age of some forms, which is 

 apparent in the marked convergence of the sides and sub-acute abdomen of the 

 old whorl, even in such discoidal species as the Psil. pleurolissum? This, as a de- 

 generative character, was reproduced at an earlier nealogic stage in the involute 

 species, as may be seen by comparing these figures with those of the involute 

 form Psil. mesogenos? The same law holds also in Waehneroceras. In Schlo- 

 theimia it becomes apparent when we compare the old age of Schlot. catenaia 

 having smooth abdomen and convergent smooth sides, with the sides and abdo- 

 men of Schlot. Boucaultiana which are similar in the nealogic and ephebolic stages. 

 Such characters are therefore retrogressive, and indicate decline in so far as the 

 forms of the whorls, the pilae, and the channels are concerned, notwithstanding 

 the fact that they are often correlated with the progressive character of greater 

 involution, and appear in the nealogic stages of some (geratologous) species. It 

 will be observed that, in Caloceras from the Mediterranean province, 4 the com- 

 pression of the whorl and other degenerative characteristics occurred without a 

 proportionate increase of involution, and that the same phenomena occurred also 

 in Coroniceras. 5 



The convergence of the sides was evidently a geratologous stage in Caloceras 6 

 and Vermiceras, but in some species of Arnioceras a slight tendency of the sides 

 to become convergent in the adult stage was noticed. In Am. semicostatum 1 and 

 tar deer escens? it occurred in the adult stage of varieties with well developed keels, 

 channels, and pilae, but not so noticeably in the lower varieties of these species 

 with less accelerated development. In Am. Bodleyi, where it was found in all 

 varieties, 9 it is noticeable at an early stage, and in the still more highly accel- 

 erated development of the involute variety 10 it appeared very much earlier than 



1 See also p. 59. 



2 Wahner., Unter. Lias Mojsis. et Neum., Beitr., III. pi. xxvi. fig. 4 a, b. 



3 Wahner., fig. 3, same plate. 4 Sumra. PI. xi. fig. 17-19. ' Summ. PI. xii. fig. 14, 15. 



6 Wahner, in the work quoted, figures several species of this genus in their senile stages. 



7 PI- ii- fig- 15. 8 P1 jj. fig 19 



9 P1 - "• fig- 23. w pi. jj. fi g . 04. 



