Clarke — The Naples F.uxa. IcO'A 



umbilicated, and having a highly subdivided suture consisting of (according 

 to Sandbergeb) not less than fourteen lobes on each ventral quadrant, the 

 majority of these being sharply acute. According to Hyatt, these have been 

 derived from the division of the fundamental ventral, lateral and umbilical 

 saddles. The type is evidently an unstable and transitional <>ne; JBeloc&ras 

 rnultilobatum attains the extreme of sutured subdivision, Bel. I\aij*eri, 

 Holzapfel, approaches it most nearly with nine lobes and saddles, w hile our 

 species, Bel. itj>i i\ bears six on each lateral slope. The increase in intensity 

 in the tendency to multiplication of these minor septal divisions is even more 

 forcibly apparent on comparison with the more stable type of Probeloceeas 

 (JPrvM. Luther i). 



Beloceras ivxx, sp. nov. 



Plate VII, Figs. 11-16. 



Shell in all external characters, as far as known, indistinguishable from 

 ProbelocerilS Luiheri. It is not so abundant a shell as that and hence its 

 various phases are less known ; but in respect t<» umbilication, ornamentation, 

 form of whorls and mature size there seems at present no means of distinction 

 in the two. The important difference is in the suture, its mature form and 

 successional phases. 



73 T9 



Figures 78, 79. Beloceras iynx. Two specimens showing the character of the later septa. x5 



The Suture. In its mature condition as show n during the course of the 

 tilth and' sixth w horls the suture is zigzagged into three acute saddles and 

 corresponding lobes; an obtuse ventral saddle is a fourth and two small 

 rounded umbilical saddles make six. While all but three of the saddles are 

 acute, only the two umbilical lobes are rounded. This is. the ultimate form 

 of the suture and it is virtually acquired at the opening of the fifth whorl. 

 During the third volution and half through the extent of the fourth, the 



