GENEALOGY. 63 
The only signs of old age observed in any specimens were the disappear- 
ance of the genicule and pile, and increasing flatness and convergence of the 
sides. 
Coroniceran Series. 
This series is composed of three subseries. 
First Subseries. —The radical form is Cor. kridion, and this species shows direct 
connection in many varieties with Arn. semicostatum. The similarities of form 
and characteristics of the young of some varieties in both species indicate mutual 
affinities, though the young of other forms of Aridion have a very different aspect. 
Three specimens of Cor. kridion from Mohringen in the Museum of Stuttgardt, 
named from their arnioceras-like forms Amm. Bodleyi, have the precise character- 
istics of an immature /ridion, viz. divergent sides, an elevated abdomen and keel, 
and tuberculated pile.* These grade into the typical Cor. kridion? having in the 
extremely young stages whorls with gibbous, divergent sides, smooth at first, 
but becoming more quickly pilated and tuberculated. 
From these forms the transitions are complete to Cor. coronaries, which indeed 
might be very properly considered as a variety of the same species, since it merely 
exaggerates all the characteristics of rzdion. From this we can pass into the true 
Cor. rotiforme,’ in which the adults differ greatly from kridion. The young * belong 
to the typical variety, and are broader and flatter on the abdomen than in hrzdion, 
and also have divergent sides and very heavy coarse tubercles. Senility is shown 
only in specimens of exceedingly large size by the very gradual obsolescence of 
the tubercles, pile, and channels, though we have not found any specimens, which 
had become entirely smooth, or in which the channels had entirely disappeared. 
The transition from Cor. rotiforme to Cor. lyra® is accomplished through a 
variety, which is separable from the former only by a single character of no 
special value. The superior lateral saddle is somewhat pointed and narrow, 
instead of being cut into on the border by numerous marginal lobes, as in rod?- 
forme. The varieties of lyra® which follow have, at an early age, a form similar.to 
that of the adult rotiforme with a more or less elevated abdomen, slightly conver- 
gent sides, and tuberculated pile. There is also a tendency to increase the 
abdomino-dorsal diameter of the whorls, the pile becoming more closely set and 
less prominent than in the first described variety.’ Senility® is indicated by 
obsolescence of the tubercles and the decreasing width of the abdomen. No 
specimens were observed in which the pile had disappeared, though in one 
specimen they were reduced to broad curved folds, and the channels were almost 
obsolete, the keel also having been reduced to a low broad ridge. This specimen 
measured 440 mm., while one at Semur measuring 525 mm. had lost only the 
tubercles, and the first senile or clinologic stage had but just been entered upon. 
1 Tf Arn. kridioides had been found on the same level with the earliest form of Cor. kridion, it would 
undoubtedly have to be considered a transitional form between semicostatum and that species; but since it is 
not found there, perhaps the safest way is to indicate the descent from semicos/atum alone. 
2 Pl. iii. fig. 3; Summ. Pl. xii. fig. 9. 
8 Pl. iii. fig. 14-17. 4 P). iii. fig. 4-9 a. 5 Summ. Pl. xii. fig. 15. 
6 Pl. iv. fig. 9-14. OP evs, Oy) Os 8 Pl; iv. fig. lo, 16. 
