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, pile, 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 Arn. 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 a 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 Psi. 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 Psi. mesogenos.? The same law holds also in Wehneroceras. In Schlo- 
theimia it becomes apparent when we compare the old age of Schiot. catenata 
having smooth abdomen and convergent smooth sides, with the sides and abdo- 
men of Sch/ol. 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 pile, 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 Cadoceras from the Mediterranean province,‘ 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.° 
The convergence of the sides was evidently a geratologous stage in Caloceras® 
and Vermiceras, but in some species of Arnioceras a slight tendency of the sides 
to become convergent in the adult stage was noticed. In Arn. semicostatum™ and 
tardecrescens,° it occurred in the adult stage of varieties with well developed keels, 
channels, and pil, but not so noticeably in the lower varieties of these species 
with less accelerated development. In Arn. Bodleyi, where it was found in all 
varieties,’ it is noticeable at an early stage, and in the still more highly accel- 
erated development of the involute variety" it appeared very much earlier than 
1 See also p. 59. 
? Wihner., Unter. Lias Mojsis. et Neum., Beitr., IIT. pl. xxvi. fig. 4 a, b. 
8 Wihner., fig. 3, same plate. 4 Summ. Pl. xi. fig. 17-19. 5 Summ. PI. xii. fig. 14, 15. 
® Wiihner, in the work quoted, figures several species of this genus in their senile stages. 
Pia. fig. 15. 8 Pl ii. fig. 19. 
® Pl. ii. fig. 23. Pl. ii. fig. 24. 
