Clarke — The Naples Fauna. 



rounded ventrolateral and a broad partly concealed dorso-lateral. The lobes 

 are three in number, and are all acute ; a small median ventral, a long, narrow, 

 sagittiform ventrolateral and a short and broad lateral. 



On the concealed or dorsal surface of the shell there are two lobes and 

 one saddle for each half of the 

 whorl ; a long, acute, median dorsal 

 lobe, a short, broadly rounded, sub- 

 1 1' u so-lateral lobe, and a broad, obtuse 

 dorsal saddle. 



Development Of Form Of Sit- Figurs 27. ManUcoceras Pattersoni. The outer course of 

 . _ TP- j CI „j TM the sutures in a normal adult. 



litres : Hirst septum. I he suture 



of the first septum is a simple curve, showing a well defined median ventral 

 lobe. This is subacute, but the lateral divisions of the suture do not 

 actually come into contact on the ventral surface as in ephebic conditions; 

 from which we may infer the absolutely ventral site and attached condition 

 of the sij)ho. 



The lateral direction of the suture is almost transverse to the dorsal 

 furrow, where it bends gently forward. On the dorsal side the suture makes 

 but a single curvature and that is median, the lobe thus formed being more 

 acute than that on the ventral surface. 



Second Septum. The curvature of the second septum is not greatly 

 unlike that of the first, the difference being in the lateral curvature which now 

 tends outward or forward and thus originating the broad ventro-lateral lobe 

 of neanic growth. 



Other P re-epliebic Sutures. The progress in the development of the 

 suture consists («) in a great widening of the ventral lobe, (b) in the pushing 

 forward of the lateral curve into a broad lateral saddle, (e) the development 

 of a dorso-lateral lobe; this is a condition shown at 2 volutions/' At 2^ 

 volutions the broad ventral lobe still obtains, the lateral saddle is narrower 

 and more prominent, the dorso-lateral lobe much broader than before and 

 rounded. 



Appearance of the Ventral Lobe, Ventro-lateral Saddle, Stibdorso -lateral 

 Lobe and Dorsal Saddle. The first of these lobes, which is so conspicuous as 

 character of maturity, makes its appearance at about the end of the third 

 volution. The form of the suture at 3 volutions, as here represented, shows 



* Volutions are counted, in this paper, from the proximal extremity of the protoconch. 



