DEMINERALIZATICN MECHANISM OF BORING GASTROPODS 59 



toward the interior of the shell (Figs. 3 and 4), and incomplete 

 holes have a central boss. On the other hand, muricid bore holes 

 are not beveled or only slightly so, are straight- walled ( Figs. 1 and 

 2), lack the central boss, and often contain shallow shelves of or- 

 ganic matrix. Circularity of the holes is obtained by the radula as 

 it is rotated on the long axis of the proboscis bv buccal muscles. 

 Size of holes varies with species and size of individuals; and form, 

 with species and with ornamentation of prev shell (Bucher, 1938; 

 Carriker and Boone, 1960; Fischer, 1922; Ziegelmeier, 1954). Al- 

 though the naticid and muricid bore holes studied to date appear 

 diagnostically distinct, the holes of many other species in both 

 families will have to be examined before this observation can be 

 confirmed. Rate of penetration of shell is approximately 0.25 mm 

 per hour in Naticidae (Ziegelmeier, 1954); rates have not been re- 

 ported for Muricidae. 



Ankel (1937) and Carriker (1961) have excised the ABO from 

 some 20 different species of lixing boring muricid and naticid gas- 

 tropods, and these glands when applied to the smooth glossy inner 

 surface of mollusk shell ( either calcite or aragonite ) produced etch- 



FiG. 1. Bore hole, 1.8 mm in outer diameter, drilled 1)\ Eiiplcuva caudafa 

 etterae in shell of Crassostrea virginica. ( X 5.) 



Fig. 2. Bore hole, 4 mm in outer diameter, drilled b\ Murcx hrcvifrons 

 in shell of C. virginica; the incomplete perforation at bottom of hole is char- 

 acteristic of this species. ( X 5. ) 



Fig. 3. Bore hole, 3 mm in outer diameter, drilled by Foliniccs duplicatus 

 in shell of Modiolus dcmissus. ( X 6. ) 



Fig. 4. Bore hole, 3 mm in outer diameter, drilled by P. duplicatus in 

 shell of Mercenaria mcrccnaria. (X 6.) 



Fig. 5. Projection microradiograph of ground section 0.7 mm thick cut 

 parallel to surface of shell of C. virginica with hole drilled by Urosalpinx 

 cinerca foUycnsis; hole 1.4 mm in diameter, and midway through shell. Stud\' 

 of the section by stereographs indicates that the inner radiolucent area (a) is 

 due to changes in the contour of the hole through the section, and that the 

 outer radiolucent region (b) is a zone of partial demineralization surrounding 

 the hole. Ti radiation; 25 kv, 50 /<. aperture. ( X 25.) 



Fig. 6. Projection microradiograph of ground section cut at right angle to 

 surface of shell of C. virginica with hole drilled by U. c. follijcnsis; section 

 was cut to one side of the hole to demonstrate zones of dense conchiolin ex- 

 tending as ledges into the lumen of the hole; the peripheral demineralized 

 zone illustrated in Fig. 5 is also shown in this section. Width of the portion 

 of the hole shown here, 1 mm. Ti radiation; 20 kv, 45 /x aperture. (X 25.) 



