my. though, is in the keelless tor til is form, the abdomen may 1" 

 elevated, or very slightly subangular. Wright's figure 1 admirably illuatratea 

 sach :m individual. The Sironotus variety figured l>\ D'Orbigny baa a more 

 compressed form and an earlier development of the keeL 



' First, those \\ bich 



eriod of the growth, and grade into the third 



' With these we find, as Bub-varieties, some which, either 



immediately before <»r at the time when the keel i- developed, change bj growth 



I form of the whorl. The abdomen m.i \ become elevated, as in the 



of some varieties of tortile, <>r depressed, assuming the as] 



v • mcII\ . those \\ li irli develop a keel at a comparatively 

 early stage, and either r«'t;iin the rounded aides, or become Bubquadragonal and 

 approximate in form and pilo 



The senile whorl had metamorphoses, which produced an elevated t>r narrow 

 abdomen, similar to thai of CaL tortile at the same stage, though in some varieties 

 r, and there is a nearer approximation to the true trigonal 

 outline- t>t' the old "i Vermiceras, 



The young ol repeated the characteristics of the intermediate forms, 



illy produced the keel at earlier periods. These are also low 



into otuer varieties, occurring later geologically, 

 which are of much lai In nil these larger specimens 4 the form is a 



."ii.il in the adult, and also has a keel, and s times faint 



channels. There is a tendency in old age t<» produce a rounded whorl, with an 

 abdomen in the clinolo resembling the Bame part in 



the ol the prominently keeled varieties of tortile and t. In 



the lai v>- also find some forms which in their clino 



. with a keel and slight channels In 

 words, there are some specimens which show a tendency in old aj 

 il form of tin- adult, very much as in the genui 

 In th the Biitures wei I in one case of extreme 



the differentiated proportions of the adult, and partially retrograde, 



1 \ • mg and the adult of many 

 • n- 'it' tin are inseparable from the 



w itli the exception perhaps ol 

 - in tli>- marginal tl 



i . i- not similar to ( / beii 



and having a verj immature gibbous whorl, which can 

 > 1 1 .- 1 1 only in variety b. In old n the broad whorl of 



ety diminished in transverse diameter, the abdomen became more 

 ■\ and pili •m. until finally n fragment "I tl 



whorl '■.mi «hed from the 



