>!\ I II. OB OXYNO BR \N« II 215 



urn. On ili«- other hand, the duration of the 

 ////. the sutures of the adult, which are simpler or more 

 arietian in outline than in ill \ hollow keel, seem to indi- 



■l independent origin directh froi '< The specimen ol 



M .-■•inn of Stuttgardt, in which the hollow keel w i. had 



shell «>f the keel remarkably thick, bul the interior evidently hollow. 

 while in tin- French specimens at Semur tin- shell of the keel was « ► f usual thick- 

 The former may possibly indicate a transition t" 

 G . however, by tin' resemblances "i the young to the adult of 

 ' ami by tin- younger period at which tin- adult charai of the 



: >.i r« • 1 1 1 1 \ a direct derivative from <>■■■ loughi I 

 - would al-o apply to Lotlutringwn, in which the young lose tin' sfriarict like 

 rely, and repeat only tin- adult form and ckaracb 

 i hnrnctcristics, tin- continual decrease in the duration of tin- adult 



nntl tin- earlier period at which tin' senile Btage of « 1 < -» - 1 i 1 1 < • makes its ap- 

 nce in each successive species, indicate that these threi 

 distinct rhe earliest representativi und in the 



Tuberculatus !»•.! a' Semur, and in tli" < Ixynotus bed of Dumortier in the basin of 

 the Rhone. The different Bpecies seem, thi i form two subseries; one 



m and its : 1 1 1 i » ■ •< . and another composed of Grenmughi, with 

 (iuitmli and Loti ind their allies, but all on th<' sami il horizon* 



Piusi Subsi I 

 Oxynoticeras oxynotum. Htati 



I'lat. I PI MM 



Amm orynntu 11: Anim - 



Amallh' tram., pi \ 



Amm 



S 



»th, and in thi- earl) I 



They may con tin and the rotundity of the 



abdomen until the specimen is 12 nun. in diameter, as figured on Plate X. I 

 Their sides then become flatter, ami slight folds ami striations appear. The re- 

 semblance ' - • decided in some iinens, thai 

 independently, no one would hesitate to place them in the same 

 allied I oily includes a clo 

 in tie / I also similar t . . the 



en in collectio J hue 



TIh- keel nppean mui 



I the normal I but in all 



I 

 I 



