The i>nl\ signs of old age obserri I in any specimens were the disap] 

 ance of the genicular and pilaB, and increasing Batnesa and convergence >>i the 



Coroniccran Series. 



Tli 



/' v . — The radical form I ridion, and this species shows direct 



connection in many varieties \sith Arn. aamcoaUdum. The similarities of form 

 and charai ■■' the young of Bome varieties in both species indicate mutual 



affinil i the young of other forma oikridion have a verj different aspect 



Three specimens of ' , kridu from Mohringen in the Museum of Stutl 

 named from their arnioceras like forms .1 B . have the precise chai 



of an immature ent sides, an elevated abdomen and keel, 



and tuberculated pila ide into the typical O \ kridum* having in the 



whorls with gibbous, divergent Bides, smooth a! 

 but b more quickl) pilatcd and tuberculated. 



irms the transitions- are compli I , which indeed 



ly considered as a variety of the same 8] 'it merely 



- all the characteristics of kridum. From this we can pass into the true 



< i which the adults differ greatly from kridum. The young* belong 



to the typical variety, and are broader and flatter on the abdomen than in /. 



and also have divergent Bides and very heavj coarse tubercles. Senilitj is Bhown 



only h edingly large size by the very gradual obsolescence of 



la-, and channels, though we have n<>t found any specimens, which 



had b ' rely smooth, or in which the channels had entirely disappeared. 



I . from f < accomplished throu 



. . which is separable from the former only by a single character <>! no 



I rior lateral saddle i- Bomewhat pointed and narrow, 



into cu the border by numerous marginal lobes, as i 



( I rbich follow have, at an earl} age, a form similar to 



• the adult with a more or less elevated abdomen, Blightly conver- 



. an 1 tuberculated piho. There is also a tendencj t" increase ih<' 



abdont of the whorls, the pil&a becoming more closely set and 



than in the lii-t described variety. 1 Senility 1 i- indicated by 



obsoli and the decn Ith of the abdomen. No 



I in which the pila had disappeared, though in one 



ncn they » i broad curved folds, and the channels were almost 



• I also having 1 n reduced t" a low bro I cimen 



; in mm., whili Semur measuring 525 nun. had lost only the 



md the fit ■ clinolog • ! but ju~i been entered upon. 



' It ! 



