250 UACI UTKS. I'll Y LLOCKKAS. 



Senequieritinus, Orh.. i> ;dso to be referred there. 

 which is distinguished by its habits from all other Turrilites. 

 and approaching very closely the earlier whorls of Heteroceras, 

 with which also, according to Pictet, it has in common the UH. 

 symmetrical build of the lateral lobes. Possibly T. Senequieri- 

 anus is only the young of what in tlie adult state is a Heteroceras 

 provided with an irregular sliat't or body. as Pietet has already 

 considered it. 



Fifty-one species. 



BACUL1TES, Lamarck. 



The completely straight Ammonites of the cretaceous have 

 been embraced in the genus Baculites and form a very good 

 natural group, which in the structure of the first lateral lobe is 

 allied to Lytocerax and Ilaini.tr,*: in fact, between a Hamites 

 with two straight limbs and a Bavuliles there is no important 

 difference. A list of species of ttunilitr.* and a repetition of 

 the diagnosis of the genus would be superfluous, MS no cluingc 

 is here made. 



Genus PHYLLOCERAS, Sut>. 



Shell discoidal. involute, with feeble sculpture, sometimes with 

 constrictions or varices, lines of growth directed forwards; 

 body-chamber short, margin of aperture simple with somewhat 

 produced lobes on the external side; no aptychus; lobes 

 numerous, diminishing regularly in size, laterals without sub- 

 division into principal paired brandies; leaves or lobes of the 

 saddles very much rounded; nntisiphonnl lobe two-pointed. 



The Phylloceratida- branch oil', according to von Mojsisovies. 

 from stems of the monophyllic Lytoceratida- of t he Trias : the 

 geologically oldest forms are still distinguished by few lobes 

 and a somewhat wider umbilicus. Within the limits of certain 

 series of forms a very constant direction of variation becomes 

 apparent in such a way that a steadily progressive complication 

 and increase in the number of saddle lobes or leaves takes place. 



Tlu- li'enus fully retains the type in the cretaceous which it 

 assumed in the Jurassic, so that a doubt as to their position can 

 never arise; namely, a reduction and simplification of t he lobular 

 line never takes place, which would seem to indicate an atlinity 

 here to the cretaceous 6V?v////V,v. ns has been thought by some 



