PLATE IV. 



Fig. 



\a. Ferisphinctes Davidsoni, S. S. Buckman, showing tlie 



mouth-border and the depression "where the test is 



removed. Zone of Steplian. Humphriesianum. Oborne, 



Dorset. My collection, one-half natural size. There are 



indications of ribs all over the specimen. 

 \h. The same, showing ventral area. 

 2a. Ferhpliindes Davidsoni, young foiTQs, showing the mouth 



border. Zone of Stephani. Humphriesianum. Oborne, my 



collection. 

 2h. Tlie same, showing ventral area. Where the test is 



removed the ribs do not seem to meet across. When it is 



on, however, they do. Natural size. 



