TTUrd & I i 'ni i' in. ' This - 



remarkable for retaining, until a lati >wth, the characteristics of the 



ind for its exceptional form, the Bidea of the whorl being 

 lingly divergent, the pilaa fold-like and heavily tuberculated, the abdomen 

 _!itl\ elevated. 

 There is one with ver) Btoul and <_ r il>t>< >u~ whorls in the 



. which cannot be distinguished from one variety of latum until a late 

 ept bj the singleness <>i' the pilaa. Single pilsa occur, how- 

 ever, in many specimens of all varieties of latum, -<> that this is not a distinction 

 of constant value. I \tum must, therefore, !><■ considered a d ndant 



om this species the transition to Cor, BucklantU 1 i- accomplished 

 by numerous intermediate forms. These exchanged the form ol in the 



aemuriense-like stage, in which 1 1 1 * - abdomen became contracted 

 in breadth, 1 1 1 « - Bides parallel, and the channels deep. This Btage \\a- retained 

 in some specimens for a long time, while in others it quickly gave place to 

 tin- huge pilaa, parallel l>ut gibbous Bides, transversely broad whorls, and flattened 

 abdomen of the adults of the typical Bucklaudt. 



In other forms, with similar young, the pilaa assumed during their adult - 



the usual aspect, with either only a trace of tubercles, <>r none. I have not I n 



able to follow the transitions of tlii*. or the - variety, into the Btoul 



V There can !>«• but little doubt, however, that the large form found 

 at L\ i n « - Regis differs only in ha\ ing had a more accelerated development : 

 skipping the double pilaa and large tubercles of the i I 



dently acquired, at a very early period in tin- young, large untuberculated 

 nml in old baracterized by a very decided narrowing and rounding off 



of the abdomen, ence and bending forward of the pilaa, disappearance of 



the channels, and a broader and lr-< elevated keel. 



The evidence <>t' transition from the riety to ' atttm 



.pon similar grounds The Bingleness and perfection of the pilaa are the 



only d which separate the young of from the young ol 



forms as variety I lults, however, the narrowness 



of the abdomen, flatness of the side-, and their convergence outwardly, are 



1 differences in aspect, which were greatly increased by advancing 

 The abdomen in some very large specimens became almost obtusely angular, as 

 in Verraiceras, and the pilaa (old like much l>'-nt forwards, and the channels 



Agassieeran Scries 

 Thi - ■ ;rn once mon to P I • has two 



/ - — Tlir 



the young of the compre* to < 



But tlii* li 



