sri'.-oKDKK I) 



ORTHOCHOANITES 



521 



crests, s&me forms having altogether .< many as fito sinuses "/<"' , >'/'/////<,///. 



tiifnifm- mill iiaitiillii large. 



i'ii,-l,ilitnit,:<, Iveinel.' ; Litiiit,:*, I'reyii I-'JLT. 1"<;7 : J /"/ ////.//>/.<, //</. 

 llv.itt. Ordovician. J //</.</ //(//>m, Boll ; IfliipH-lmi-thoceratf Kernel.'-. ()I-IM\ ician an-l 

 Silurian. (For re-descriptions see Hyatf s /'/<///"/ ////. 



III. I'I.KI BONAUTItTDA. 



Comparatively smooth nn uti/ini/i,.^ (I,,- ///////////-. .//,,-/> il/'.<n,i,l,il I,, if hui/imi nj, t<, 

 some highly involute shells in the Trin*. Tin' lt,r M, .>-.,,!< ,1,1,1 y ',///,/,// x/,,//, 

 nil ilnji/ij iiti-nliitr. XOHII- of tin-. Triassic ClydonautHidck /<"/, ,,,,-. sinuous tutw 



n iinnti-r a a mini- of lobes and s<t<l<ll'* tlmit mi ntln-r A"'"'////'/.<, null tins cum fill .: it a 

 jii /-x/x/x, <i!tl>n<ili to a, lesser degrt'f, n/noml tin .//'/v/xs/V, ('ntn,;,,,!.-;. <m<l Ti-rtin ril form*. 

 tiihiilnr mill x///^//, with most! if xlmrt fniun-l.< except in Aturi'i. /'//./-,- //,/ /-. 



K;iniily 9. Grypoceratidae. 



Primitive forms have di&coidal volutions ?'//// //// x//,//y/c .<//// /.>-, ///// af< .^n-,-, ,,/,,/ 

 In! i /I ml uti; shells having more complex sutures. Tlie latter have prominent //)//</ 

 *, t< 1, 1 1,:* sometimes divided by a lobe, and large lateral and dorsal lobes. All genera 

 save one known to have annular lobes. Shells less hiylilii oni<n,t,',it<'<l flum /// j,i;;;;lin,j 

 f n in if it, n ml sutures simpler than in the next following. 



SynngoceraSj Hyatt. Discoidal with primitive, approximately tubular, or .slightly 

 compressed volutions. Surface marked by longitudinal ridges, sometimes intersct-tiug 

 the transverse lines so as to produce a cancellated surface. Sutures with faint ventral 

 saddles, slight lateral and dorsal, and minute annular lobes. Siphunrlr Any .-mall 

 and near the venter. Trias. 



Grypoceras, Hyatt. Volutions more or less deeply involved, but umbilk-u- <>pni, 

 the venter narrow and often channeled. Sutures 

 with narrow, sometimes deep ventral lobe, broad, 

 sweeping lateral lobes, and deep dorsal with 

 annular lobes. Siphuncle dorsad of centre. 

 Trias. 



Family 10. Clydonautilidae. 



Jiave folds in some species, and all are 

 ili-i jilii i a ml a 1 1' I'.rcept the primitive genus Clymeno- 

 in i n til n^. Lateral lobes of sutures more or less 

 //if/ n ml often sub-angular, suggestive of the 

 e among Ammonoids. SOUK- //A////// 

 a ml involute species have the umbilical 

 lobes exposed on the sides, and an additional pair 

 of litt'riih developed near the vent>/\ tin* mnL-i/ni 

 three pairs of lobes on each side. The compressed 

 volutions, narrow venter, and aspect of the young 

 mill primitive forms seem to indicate close djini/fii 

 with the Grypoceratidae, but only a few species of 

 luft Mesozoic timeare knon-n to hnr<' <ninnl<tr lobes. 



FlG - 10C8g 



S1> ' 



Clymenonautilus, gen. nov. Smooth, dis- 

 coidal shells with more or less compressed J 

 volutions, and narrow convex venter. Sutures 



with prominent ventral saddles, one pair of deep lateral lobes, and large marginal sa< Idles. 

 Siphuncle supposed to be near the venter. Type C. (Xaut.) Ehrlichi, Mojs. sp. Trias. 

 Mojs. Deeply in\<ilved nautilicones with compressed volutions, 



