part ■!■] EVOLUTION OF THE LIPAROCKKA TI D.K. 2S? 



(2) With a fold passing straight across the venter, the rib-curve being 



indicated by striations only. 



(3) Without folds on the periphery ; curved striations only. 



It does not seem necessary at present to create new species for 

 these forms. 



OrSTOCERAS ALLCEOTYPUM, Sp. 110V. (PI. XXV, figS. 1 a & 1 B ; 



text-tig. 12 ft, p. 285). 



Dimensions :- 









Diameter. 



Whorl height. 



Whorl thickness. 



Umbilicus. 



90 mm. 

 45 



40 per cent. 

 35 



37 per cent. 

 35 



38 per cent 

 44 



A heterogenes-tike form (morphic equivalent of Androgynoceras 



hybrid a) with Capricorn ornament on the inner whorls, the last half 

 of the outer whorl swollen and having more slender costae and two 

 rows of tubercles. The forward curve of the ribs on the periphery 

 is clearly shown. 



Capricorn ribs are retained until a diameter of 70 mm., when 

 the shell is scarcely different from O.Jtgulinum. The cost;e are 

 regular up to a diameter of 40 mm., after which they are more 

 widely spaced. Two rows of tubercles are present on the outer 

 whorl, but those of the inner row are very feeble. The ribs divide 

 at the outer tubercles, passing with a sharp bend across the 

 slightly-angular (convexi-fastigate) venter. Suture complex, but 

 on the same plan as Oistoceras omissum; deep and narrow external 

 lobe with a high median saddle, half as high as the external saddle. 

 This latter is asymmetrically divided, being deeply undercut on the 

 dorsal side. The first lateral lobe is nearly as deep as the external 

 lobe, and is terminated by three unequal lobules. 



Occurrence. — Lower margaritatus zone, Bracebridge (Lin- 

 coln). 



O. alloeotypum is distinguished by its whorl shape from its 

 morphic equivalents in other series, its suhangular venter most 

 resembling A. Jiybrida. Its generic position is indicated by its 

 peripheral rib-curve and its suture. 



F. Becheiceras, gen. nov. (See p. 2(33.) 



Bechetceras bechei (Sowerby). (Fig. 13, p. 288.) 



Compare Ammonites bechei A. d'Orbigny (3, pi. lxxxii) and Mgoceras bechei 

 Wright (8, pi. xli, figs. 1-2). 



A. bechei, formerly considered by many workers to be synony- 

 mous with A. striatus or A. henleyi, lias generally been applied in 

 more recent years to the finely-ornamented sphserocones of several 

 series of the Liparoceratidse. The sutural characters pointed out 



(fig. 1 b, p. 258) restrict the name to ammonites of the Becheiceras 

 series onlv. 



