Clarke — The Naples Fauna. 



133 



In the mature whorls, the fifth and sixth, the cross-section, as already 

 observed, becomes similar to that of the associated discoid species of goniatites, 

 Probeloceras Lutheri, P. (?) Naplesense and Beloceras iynv, though less 

 elongate and with a narrower peripheral flattening. 



The Suture. We have not been able to determine from our material the 

 character of the first suture. Bkaxco has recorded it as a simple asellate curve, 

 while the second suture has a broad ventral lobe. At two and three-quarters 

 volutions, C. neapolitcmd has a broad and deep, but acute, ventral lobe, and a 

 broadly curved lateral lobe, while the lateral saddle is narrower, transecting 

 the ventrolateral shoulder of the whorl. On the dorsal side of the whorl is 

 a deep and narrow median lobe and a shorter and obtuse dorso-lateral lobe. 



At three, four, and four and one-half volutions the sutures show a gradual 

 increase in the relative size of the ventrolateral saddle and the lateral lobe, 

 and in the mature suture the former has become broader and deeper than the 

 latter; the ventral lobe also appears to be minutely divided at its apex form- 

 ing a ventral saddle. On the dorsal side the dorso-lateral lobe has become 

 acute with a sinuous outer curve and the dorsal lobe is very narrow and sharp. 



TJie Sipho. Bkaxco has observed that the position of the sipho at the first 

 septum in 0. cf. undulata, Munster, is ventral; this we have also found to be 

 the case in C. neapolitana, without having been 

 able to determine the mode of subsequent 

 change in position. It is clearly evident that 

 the sipho becomes dorsal in its position in the 

 course of the first volution. As to the con- 

 tinuity or discontinuity of this tube, a feature 

 upon which Gumbel based the main division 

 of the Clt/menice, our material affords no 

 evidence. 



Omamentcttion, The protoconch has 

 shown no trace of surface ornament but the 

 first whorl is covered with close, transverse, 

 elongated lines. During the course of the 

 second whorl appear the distant curved lamellar processes which take 

 the form of a varix with its concave surface projected forward, expanded, 

 and when fully preserved, almost enclosed at the anterior margin. These 

 varices have their greatest height at the dorso-lateral angles of the 

 whorl and abut against the surface of the succeeding whorl. They have either 

 not extended over the ventral surface of the whorl or have become resolved 



Figure 106. Cyrtoclymcnia neapolitana. 

 Development of neptal sutures. 



