274 



DE. A. E. TRUEMAlSr ON THE 



[vol. lxxiv, 



the whorl height of the capricorns of Amblycoceras and Oistoceras 

 at the same diameter ; the whorl shape, however, does not differ 

 markedly from that of Liparoceras sparsicosta until the diameter 



Fig. 5. — Sutural development of iEgoceras 

 latrecosta (Soicerby). 



h 

 50 mm. 



9 mm. 



f 



7 mm. 



e 

 4 - 5 mm. 



d 

 3*5 mm. 



c 

 0-7 mm. 



b 



a 



[a-g, W. D. Lang Coll. (figured in PI. XXIII, fig. 4). 

 h=Specimen figured in PI. XXIII, fig. 3 : W. D. Lang Coll. No. 1566.] 



of 10 mm. is reached, when JEgoceras latcscosta is less depressed. 

 Low folds appear at a diameter of 3*5 mm.; but there are no ribs 

 on the periphery until the shell is nearly twice that size, only 

 becoming fairly prominent at a diameter of 11 mm. 



)iameter. 



Whorl height. 



Whorl thickness. 



Umbilicu 



mm. 



per cent. 



per cent. 



per < cut 



•84 



43 



79 



2(5 



1-2 



40 



67 



32 



2*5 



40 



68 



P40 , 



42 



35 



67 



52 



8-0 



35 



50 



4U 



14-0 



29 



36 



46 



The early sutures of the Capricorn forms are similar; indeed, the 



