7 



PLATE VIII 



PHYLOGRRONTIC CHARACTERS 



FIG. I. Parkinsonia dorsetensis (much reduced). Bathonian, Burton 

 Bradstock, Dorset. The inner (early) whorls are strongly 

 ribbed. Gerontic laevigation obliterates ornament in the 

 outer whorls. 



FIG. 2. Clavella longacva. Eocene, Barton, Hants, The protoconch 

 is followed by one whorl showing "Fusid" cross-ornament. 

 The two next, whorls are smoothed by gerontic laevigation, the 

 rest become secondarily spinous by excessive calcification 

 (based on Grabau's figure). 



FIG. ,3. Clavella solanderi. Eocene, Barton, Hants. A type similar to 

 C. longaeva, but failing to progress beyond laevigation. 



FIG. 4. Phillipsia gemnmlifera (after Woodward). Carboniferous Lime- 

 stone. Showing gerontic features in simplification of the 

 glabella, multiple pygidium, and pustular ornament. 



