sri!-oKi>KK 



CVKTOCHOAMTKS 



Mill. Like tin- la-t l.tit more ;iivn;iti-, with laterally <-oui r. t ,-t.-.| 

 aperture. .UK! a short hyponomir sinus distiiirt tViiiu tin- I'l-arhial area. Silurian. 



Family 1). Trimeroceratidae. 



Smooth breviconic orthoceracones and cyrtoceracones *//////// i<> /'.,/-//-.-., 

 n<l nut H />'*, but more slender, e*j>-/<i!li/ in tin /////////, <m<l <////<'/- -./;/ ili.<ti,,,-t in 

 primitive forms. Even the lntt>-r nxnullii Inn;- linn-ln'iil r//.--/ //////// ///<///./ '///" /row 

 hyponomic area by ingrowth of sides of the aperture, and in all spec /-/ //.-,,/ ../,,//.< ///< 

 hyponomic sinus and s}n<-inl i njlfctions known as " l>,-in-lii<il sinuses" an f<> ////"/ /'^ /'><.< 

 o/ <Ae arms o?i etfo/es o/ brachial area. /-V//^////, Mr HJH rtun' hmmns /,<///<,</ /,, ,, /,/,,/- 

 or iess F- o?' T-shaped fujnn\ n-ith. an open st>mi<-; r<-nl<i , >/'// ;/x /// //* -,,,/ o/' ///- hyponomic 

 slit or area, and similar sinuses in the edges of tin In-m-lu'iil .<///. / /v-xy/o//'////// // //<>: 

 number of arms. All Silurian. 



Mandaloceras, Hyatt (Dimorion, Ban-.), (Fi^. 1084). Dill-rs JVum Potariocerat in 

 the gerontic aperture, which is laterally c<>nn-art<-<l, and lias h\ -jMinnmii- and l>ra<-lnal 

 areas distinctly dift'ereiitiated in all Imt the nn>l jriiniti\f 

 species. More specialised forms have, llicsc an-a.- narrn\\t-<l 

 down, but special sinuses are not formed. 



FIG. 1084. 



Min<ilii!<ii-i'rti.-<(<;<iiiij>li.) l:<ili> niii-inii, JJarr. sp. Silurian (EtageE); 

 Dvoretz, Bohemia. ^4, Side view of conch. J5, Aperture. 



. 1085. 



sji. Silurian (E) ; Dvoretz, 



Holieniia. '/i (afti-r Hairaii'li-). 



Trimeroceras, Hyatt (Trimorion, Trimeres, Barr.) ; Pentameroceras ; Septameroceras, 

 Hyatt. Silurian. Aperture in the lii-st has a median and two ln-arhial ; in tin- 

 second .a median and four l>ra<-hial ; and in the last a median and six l>rarhiul 

 sinuses. 



Hemiphragmoceras, i^en. nov. ( 'oni]ireed endo^aMrie ''vrtoceracones having a 

 narrowed hyponomic area like Phragmoceras, luit with brachial aivas as in Dimeroceras. 

 Type H. (Phrag.) pusillum, Barr. sp. 



Tetrameroceras, Hyatt (Tetramorion, Tetrameres, Barr.), (Fig. 1085). Like the la.-t, 

 but with more highly conti-artt-d ajieriun- and tour lateral sinuses. 



Hexameroceras, Hyatt. Bracliial area with >i\ lateral sinuses. Octamci' 

 nov. Brachial area with eight lateral sinuses. Type 0. (Phragm.) ctiUiatonin. \\.\\\\ >p. 



Kamily 10. Phragmoceratidae. 



Smooth breviconic cyrtoceracones and gyroceracones rapid! // ,.< i> mUmi /// (irn-Hi in 

 their dor so-ventral diameters, and Imrinn </ n iipi-rim;:-: ,,/<// in y//-///*/V/Vr ///y/-x ./ tin- 

 young and ephebic stages of more specialised forms. In tin- (<itf>r <j< r<niti<- i>< rfures are 

 laterally contracted and have a very l>mj lu/ponomic area terminated b;i <( lury 

 hyponomic sinus. The brachial area may be more or less open and elliptical) or 



