PLATE VI 



ONTOGENY OF SIX SPECIES OF cEBiTHiuM (Continued) 



Fig. 1. Cerithium tuberosum, thirteenth volution. 12 x11.5 mm. 



Fig. 2. Cerithium tuberosum, fourteenth volution, 24 X 29 mm. 



Fig. 3. Cerithium tequispirale, fourteenth volution. 9.5X9.2 mm. 



Fig. 4. Pseudovertagus aluco, thirteenth volution. 19 X 11 mm. 



Fig. 5. Pseudovertagus aluco, fourteenth volution. 22x20 mm. 



Fig. 6. Cerithium lamellosum, aperture. "12 X 11 mm. 



Fig. 7. Cerithium retardatum, fourteenth volution. 8.5X4 mm. 



Fig. S. Cerithium retardatum, aperture. 7x9mm. 



