288 



DE. A. E. TRTTEMAaST OX THE 



[vol. lxxiv, 



A typical example of Becheiceras bechei was obtained by 

 Dr. Lang from the Upper Limestone {Oistoceras sub-zone) of 

 Dorset (W. D. Lang Coll. No. 4073). This remains smooth until 

 the diameter of nearly 20 mm., when it becomes finely bitubercu- 

 late ; the Capricorn stage through which this series presumably 

 passed is omitted in development. 



There is, therefore, little change in whorl shape. 



Diameter. 



6 mm. 

 12 

 28 

 41 



Whorl height. 



46 per cent. 



50 



56 



53 



Whorl thickness. 



67 per cent. 



58 



56 



53 



Umbilicus. 



16 per cent. 

 11 



Fig. 



13. — Sutured development of Becheiceras bechei 

 (W. D. Lang Coll. No. 407 S). 



b 

 19 mm. 



a 

 7*5 mm. 



Ammonites which constitute an earlier stage in the JB. becliei 

 series occur in the dceclalicosta sub-zone of Dorset ; they have a 

 somewhat wider umbilicus than B. bechei. 



It has already been indicated that B. becliei is very similar to 

 certain finely-ornamented forms in other series. The following 

 points of distinction are useful : — 



(1) The sutural proportions (text-fig. 1 b, p. 258). 



(2) At all stages in development the whorl thickness of B. becliei is less 



than in corresponding stages of Liparoceras. 



(3) The young of B. bechei is smooth for a longer period than the young 



of other forms. 



G-. Pari^odiceras, gen. nov. (See p. 264.) 



Pakixodicekas eeineckii (Quenstedt) (4, pi. xxviii, fig. o). 



A compressed sphserocone with smooth inner whorls (no Capri- 

 corn stage). Bituberculate, tubercles paired, regular, nearly forty 

 in each row, the two rows widely separated. The ribs do not 

 divide on the lateral area, but divide into two or three on the 



