Clarke — The Naples Fauna. 65 



constrained to assume, for reasons already stated, that further growth would 

 have intensified rather than have lessened the carination of the whorl. 

 This is a feature which would place the shell at a different stage of pro- 

 gress than such forms as cur Ma/nMc. simulator, the Sandbeegers 1 and 

 TscHEKNTSciiew' ? iron, carina 'vs. 



Manticoceras rhynchostoma, sp. nor. 



Plate IV, Figs. 6-13 ; Plate V. 



The Adult. We have found that in Mantic. Pattersoni the ephebic con- 

 ditions accompany an approximation to dimensions which are well represented 

 by the figures given on Plate I, and embody from five to six volutions of the 

 shell. There are, naturally, slight individual variations in size of shells at any 

 given growth period, but it is apparent that in Mantic. rhynchostoma the size 

 of the shell at any definite number of volutions is greater than in Mantic. 

 Pattersoni) hence, the shell of the former at the average adult dimensions of 

 the latter, presents fewer volutions than that. In the general aspect of the 

 two however, even close inspection of the exterior will usually 

 fail*as a basis of distinction, but attention may be directed to 

 the following facts : in Mantic. rhynchostoma the lateral slopes 

 of the conch are more convex and the venter is sharper at its It^Manticoc^as 

 periphery though considerably broader just within this curve. [&« fourth voju- 

 These are but slight distinctions nor are they supplemented 

 in any degree either by the character of septation or the nature of umbili- 

 cation at such grow th stages. Let, now . vertical sections be made through 

 the umbilicus of such equi-sized specimens and their fundamental difference 

 is emphatically declared. 



The Protoc<»i ch : Immature Phases. The protoconch in Mantic. rhyn- 

 chostoma presents no features by which it can, when isolated.be distinguished 

 from that of Mantic Pattersoni. On a comparison of the figures here given 

 this is sufficiently evident without further comment. 



The Xcpionic Stage. Here we meet w ith the same smooth condition of 

 the conch extending for rather more than a half volution and terminating in 

 a rounded varix. The phases of the nepionic stage which have already been 

 noted as defining the ana-, nieta- and paranepionic conditions in Mantic. Pat- 

 tersoni are as clearly marked here. 



Post-nepionic Stages. \Yith the close of the nepionic condition the dif- 

 ferences from Mantic. Pattersoni make themselves evident. The varices 



5 i 



