kgp] 



HKTEROCERA8, .l' ',!,. 



// embrace- ;i number of form- ..I' very peculiar 



-hape. \\ Inch -land iiithe-ame !-rl;iiinn tn /'/ - 'I'urri 



to //'//////>-. Our genus differs from tfrtocero* in departing 



from the -piral coiled in one plane, from '/'// //////,* in it- a-\ in 

 met rieallx divided lateral lobes. I. nt be-ide- this in it- whole 

 habit ii- :in<l it- quite abnormal curvat HIT. known from tin- figure- 



of d'Orbimiy. I'.r-i.ic- tin- ilm-r tv|>i<-:il -pccjc-. Twrrttite* 



'jiii'-ri. il'Orli.. i- :il-o t<> ! |l:icc| IUMT. 

 Hi kB l-iMKisn-n. d'Orh. T. 101. lig. 532. 



9aof ASPIDOCERA8, Zittel. 



|-:\tt-rn:il form very v:ri:illr. soinct inics tl:it with wide umhili- 

 CllB, sometimes inflated with :i niirrow uinbilicus ; cxtennil side 

 ronnde<l or with :i l>ro;id external furrow, never with :i curinu or 

 :inrK'. Seiiljitnre cnisisting of OIH- <>r two rows of tubercles or 

 w:inlii!Li. Tubs, as a rule, present only in the young state. 

 Margin of aperture simple (A*p. aporum with ears'/). lody- 

 eliainl>er short. I'inbracing two-thirds of a whorl. Cellulose 

 Mptyelii. Lol.ular line tolerably simple; siphonal, two laterals, 

 al-o often (in tin- ^eoloo-icnlly younger species) an auxiliary 

 lobe. Lobes not much cut ( wit h the exception of Asp. Altenenxe 

 and drcumspinosum) ; bodies of the lobes and saddles broad. 



The development of A.<j>i docercLS is pretty well known; the 

 branrhinii' otf of Perisphmctes seems to take place in the ni>per 

 Callovian. If one breaks away the outer whorls of one of t he 

 -impler. geologically old types, for example Asp. perarnt a/7n . 

 one find- wit hin a kind of sculpt ure. which leaves no doubt in 

 regard to the origin of the groups l^'ritjthinctes auri'irrn* and 

 -'<!; curved ribs and tubercles are identical in both, and 

 the last are developed into the external row of t ubercle- of A*i> /- 

 docerti*. amongst which tin- forms with but one external row of 

 tubercles represent the original type, from which the bi-tubercu- 

 late IVrarmata are tirst developed, which in theyoun 



rdiiiLi to the staii'e of the ribs and tubercles, pa-- through a 

 'lid with only an external row of t ubercle-. then delinitelv 

 the third with two rOWS of tubercle-. 



To the large -erie- of I'erarmata with double series of tuber- 

 cles, which have no auxiliary lobe, -everal other series ale allied ; 



