J. G. WALLER ON CLIOKA CELATA, ETC. 267 



The recent discoveiy of an Annelid, on one of my slides, taken 

 from a shell with burrows, comes in aptly for my conclusion. It is 

 similar in size to the dried form alluded to, and in its figure 

 (PI. XXI., Fig. 8) I have marked near its head where the diameter is 

 the 2,000th of an inch. The remains of two others coiled up within 

 circular burrows, in diameter the 333rd of an inch, I have also found 

 and preserved with the small fragment of shell itself. 



DESCKIPTION OF PLATES XX, XXI. 

 Plate XX. 



Fig. 1. — Drawing of a portion of oyster shell full size, showing the orifices. 

 Fig. 2. — Ditto, ditto, of the limestone pebble from Babbicombe, showing its 



minute orifices, and the excavated cups denuded of the outer 



crust Actual size. 

 Fig. 3. — Orifices of the Sn^l^/tus^horlngi from an example in the beechen 



cover of a book, dated 148-t. Actual size. 

 Fig. 4. — Drawing of a vertical sectiou of oyster shell, showing burrows. 



Magnified about three diameters. 

 Fig. 5. — Burrows in Babbicombe pebble. Three diameters. 

 Fig. 6. — Burrows of Scolytus. Section taken from the covers of the volume 



referred to. Three diameters. 

 Fig. 7. — Drawing of sub-circular depressions, as seen in excavations in 



oyster shells 95 diameters. 

 Fig. 8. — The same as in Babbicombe pebble. 95 diameters. 

 Fig. 9. — Same as in the beechen covers of the book. 45 diameters. 

 Fig. 10. — Geometric plan of the mode of excavation. Tlie dotted lines 



exhibit portions of the circular boundary effaced by the adjoin- 

 ing subsequent excavation. 

 Fig. 11. — Plan of excavation in Babbicombe pebble, a. Shows cups in 



section, with orifices and extension of burrows. 6. Cups 



denuded, showing small orifices at bottom for extension of 



burrow. 

 Fig. 12. — Portion of oyster-shell, showing similar minute orifices, as in the 



pebble referred to. Actual size. 



Plate XXI. 



Fig. 1. — Excavated channel in section of oyster shell, 100 diameters. The 

 diameter of extreme point measures 2,000th of an inch. The 

 smaller excavations, cut through at right angles, have the same 

 measure. The shaded part is debris caused in making section. 

 Fig. 2. — Orifice cut through periostracum of shell. 75 diameters, 

 Fig. 3 — Portion of lamina of oyster shell, with early development of the 

 sponge. About 15 diameters. 



