No. 490] 



643 



Strong spirals appear on the body of the whorl without the forma- 

 tion of spines, one or sometimes two of these spirals appearing 

 above the suture of the succeeding whorl. Intercalated spirals 

 occur on the body of the last body-whorl.^ 



These :\rehinias therefore seem to be extremely accelerated, the 

 spines appearing while the ril)s are still in full force. 



found" in .\I.\lach/li'is L(>a from the Philippines (Martini (lienmitz 

 Melaniapl it. fiu^ _> an<l _>a in ^^ hi. h t^^ u ImrK of the ad.ilt are 

 marked In narrou (res.entie lil.x aiu < Hat. d In numerou. ^jHrals 

 which appear in the earliest part of tlie ril)l>e.l whorls. The initial 

 whorl is not known but the whorls imme.liat.-ly succeeding are 

 smooth in appearance and embrace to the anibiius. Whether or 

 not fine spirals occur on the earliest whorls is not ascertainable. 

 The succeeding whorls embrace less, thus producing tlie .slender 

 sj)ire. In the adult of many individuals the ribs become olxsolete 

 that being the usual line of development. Brot (Martini Chemnitz 



ac(|uires two r.nvs of tul)ercl.-s in th.>' adult thus |)aralleliu<r M. 

 asprra/a var. ,V of the Piiilippin.v., 



WUUv thcM- txpe. sh.m au-iadationai prouressi,,n. modifie.l l.y 

 ditferential acceleration and retardation, other species referred to 

 Melania show degradational progression, i. e., a progressive modifi- 

 cation through suppression of characters. Certain Jurassic Pseu- 

 domelanias sliowing this have already been mentioned. A modern 

 example is Melania elcvata Say from Indiana. Here the late 

 nepionic and neanic whorls are carinated, this carina gradually 

 disappearing the shell becoming smooth and with scarcely im- 

 pressed suture and with spirals only on the lower part of the whorl. 

 The aspect is that of Pseudomelania, the character being derived 

 through progressive reduction of features inherited from specialized 

 ancestors. 



The .same thing is true of M. drshaijsiami Lea, and M. m.siu- 

 lata Lea from 'lVnnes>re. lien- i\w ord.'r of dev.-lopuu'ut >o.-ms 

 to be entirely invcrte.l, the carii.-^t whorN being carinatcil while 

 the later one^ show sn.ce-ive sup].re^>ion of the . ariua. and the 



