CONCHOLOGY. 21 



considerable calcareous support, funnel-shaped, penetrating 

 the bodies to which the animal is attached. 



Creusia stromia. Creusia spinulosa. 



C. verruca. 



C. spinulosa. The spiny Creusia. 



Very depressed, striated, sometimes with marks of divi- 

 sion into four pieces ; operculum bivalve. 



C verruca. The warted Creusia. PL 4, fig. 2. 

 Whitish, slightly depressed, w^ith interwoven obliquely stri- 

 ated valves ; the margin at the base irregularly serrated. 



6. Pyrgoma. One species. 



The principal difference between this genus and the Creu- 

 sia is in form. 



Shell sessile, rather globular appearance on account of 

 the valves being more closely united, ventricose, convex 

 above, apex perforated, aperture small and elliptical ; oper- 

 culum bivalve. 



P. cancellata. The cancellated Pyrgoma. 



Thick, conical. Patella-shaped, ribs radiating from the 

 summit to the base ; aperture very small, closed by an oper- 

 culum of which the two pieces are long and narrow on each 

 side ; pale violet colour. 



7. Anatifera. Five species. 



The shells of this genus and the three followmg genera 

 are affixed to marine bodies by a tough membranous pedun- 

 cle, varying in length. 



Shell flat, with five valves imbricating more or less on the 

 edges, united by a thin membrane. 



Anatifera laevis. Anatifera dentata. 



A. villosa. A. striata. 



A. vitrea. 

 A. IcRvis. The smooth Anatifera. PI. 4, fig. 5. 

 Five smooth valves ; the dorsal one rounded at the sides, 



