ORDER II 



A.MMONOIDEA 



TABLE SHOWIXd I'KINVIl'AL DIVISIONS OF THE AMMONOIDEA. 



Infra- 



f 



d; - 



, Zittel. 



Xl.w Sri:-Oui.Ki:>. 



Gastrocampyli I. 



II. 



Eurycampyli 

 Glossocampyli 



sipkoZ'ta, 1 ^ocampyli 

 Zittel. 



Phyllocampyli 

 Leptocampyli 



Pachycampyli 



IV. 



KM I LVALENTfl i M'l.i: F. u:\ii i: - 



< 'I,!, i,,- n in. < 'lijnicnidae (Clymenioids). 

 ciii: ib-order. Devonian. 



Goniatitcs, Goniatitidae (Goniai i ; 

 /ygous inflections entire only in >impl-- 

 form.-, becoming divided and .similar to Ceratitoidfl only 

 in some highly specialised o-ncra ,,[' the rermian and 

 ) Trias. The young are aaellate in radical form>, becoming 



lati.-ellate in more -peeiali-ed X''ii--r.i. Mostly I). -vonian 

 I and Carboniferous ; comparatively few IVrniian p-prc- 

 Isentatires. 



Ceratites, Ceratitidae (Ceratitoids). 

 Zygous inflections entire only in a few radical forms, 



probably derived from the same radicals as the I'lnjllo- 



campyli. Lobes become divided b\- line marginals 

 j forming serrations, but bases of saddles remain entire 



except in highly specialised genera. Supposed to be 

 i mostly latisellate, becoming angustisellate in specialised 

 I forms. Triassic. 



f Ammonites, Ammonitidae (Arnmonitoids). 



Zygous inflections entire only in Palaeozoic radicals of 



the Phyllocampyli. Lobes become divided by fewer and 

 I larger marginals than in Ceratitoids ; bases of saddles 

 -{ remain entire only in simpler forms of the Trias.sic 



Phyllocampyli. All others have completely divided 



inflections except some of the degraded Pachycamj> //?<'. 



Phyllocampyli range from Devonian to Cretaceous. The 

 .last two sub-orders are Jurassic and Cretaceous. 



Sub Order A. GASTROCAMPYLI. Hyatt. 



Conchs varying from forms like Anarcestes to those that are more or less compressed in 

 section, and from completely discoidal to compressed and highly involute shells, thu swrfoct 

 being either smooth or with luni*' urines. The characteristic ventral saddles are alnnj.<t 

 imperceptible in some primitive species, and although entire and large as a rule, are in 

 some genera divided by entire ventral lobe*. S> />f" concave /<///</ tin' m>#il j>hin,'. 

 Siphuncle dorsally situated. Liritui <-Ji "///// <<< upying about three-fourth* f mliifivn . 

 aperture with hyponomic sinus. 



The ventral saddles are dc\cl ij.cd 1>\ tin- obliteration of primitive ventral lobes 

 and fusion of the first pair of saddles (Branco). It is at present questionable wln-ilu-i 

 the ventral lobes of some genera HI-- secondary modifications or retention- of th<- 

 primitive ventrals, and also \\lirtlirr tliesi- can In- regarded as di\ ided vciitrals even in 

 the Cymadymenidae. The anti>ipln> :a! loin- i- lai^e and long, and ot'h-n fusc<l with 

 the siplumcular funnels, whieli are long and single (monochoanitic). The dorsal .-mum-, 

 so far as known, are very peculiar, lias ing only a pair of large saddles confluent with 

 the last pair of external saddle- ; or one pair of zygous saddles, and one pair of xygous 

 lobes, the second pair of zygous saddles being confluent with the innenno-t ,-\ternal pair. 



The perforation through the umbilicus, so constant in Nautiloids, is absent, and so 

 too are the umbilical depressions on either side of the neck of the protoconch, common 

 in other Ammonoids. The forms are nevertheless amnioniti< ones, having the pmto- 

 conch and other characters of the order. The first septum is described as asellate 

 (Branco), but figured as having a broad saddle on the venter. 



Family 1. Clymenidae. ({umbel (<;?/rm/). Primitive, forms similar to Anar- 



