96 DEPARTMENT OF THE NAVAL SERVICE 



8 GEORGE V, A. 1918 

 Bathymetric Range. 



There is but little information on the depth to which Teredo can work below low 

 tide level in Canadian waters beyond Murphy's^ photograph of a piece of bored spruce 

 which was submerged two years, four feet below low water at Pictou, N.S. At Woods 

 Hole, Mass., it has been found living at a depth of 13 fathoms^ and in New York 

 harbour at 25 fathoms.^ Three well-known rock and clay-boring molluscs are found 

 in the same general region with Teredo navalis. These are: — 



Petricola pholadifoi-mis. 

 Zirfaea crispata. 

 Saxicava arctica. 



P. plioladiformis appears to be most common near the inter-tidal zone, but it has 

 been dredged at a depth of 30 fathoms in St. IMarys bay by Dr. A. G. Huntsman. The 

 recorded range of Z. crispata is from low tide to 70 fathoms in Canadian waters. Off 

 the Maine coast it is recorded by VerrilF at from 22 to 44 fathoms. At Woods Hole 

 it also occurs at a considerable depth below low tide. Saxicava arctica is another rock 

 boring shell which has a considerable range below the tide line. On the Iceland coast 

 it is found between tide marks^ while off the Labrador coast it is common at 10 to 50 

 fathoms.^ 



Honeyman reported limestone boulders bored by Saxicava which were found at a 

 depth of 65 fathoms off the Nova Scotia coast. ''^ 



The rock-^boring habit gives to molluscs which practise it a special geological 

 significance, as pointed out by Barrows.^ The rock cells of such molluscs gradually 

 expand as the rock is entered from the small aperture on the surface drilled by the 

 very yoimg shell into chambers corresponding to the size of the adult molluscs which 

 thus leave no avenue of escape for the shell even after its death. The improbability 

 of the removal of boring shells by current action to waters deeper or shallower than 

 the living animal occupied permits the fossil molluscan rock-boring shells to yield 

 information which is precise within the limits of their vertical range concerning* the 

 depth of the sea in which they lived. 



DISTRIBUTION. 



The genus Teredo has a wide distribution around the coasts of the North Atlantic. 

 None of its several species however belong properly to the Boreal fauna although 

 there are outlying colonies of some species which are surrounded by the boreal fauna. 

 T. norvegica, which is the prevailing indigenous species on the eastern side of the North 

 Atlantic, affords in its European distribution an interesting example of such discon- 

 tinuous distribution toward the northern limits of its ramge. This species ranges 

 through the Mediterranean and up the west coast of Europe into the waters of 

 S.W. Norway. But G. 0. Sars^ states that "the only place inside of the Arctic 



1 Proc. and Trans. N.S. Inst. Nat. Sci., Vol. 5, 1S81, p. 376, fig. 4. 



2 Summer, F. B. Osburn, R.C., Cole, L. J. A Biological Survey of the Waters of Woods Hole 

 and vicinity. Bur. of Fisheries, Bull. 1913, Vol. XXXI, Part II, Sec. Ill, p. 702. 



3 Proc. and Trans. N.S. Inst, of Nat. Sci., Vol. V, 1881, p. 376, fig. 14. 

 * Am. Jour. Sci., Vol. 7, 1874, p. 503. 



5 .Johansen, A. C. On the Mollusca between tide marks at the coasts of Iceland. Videnska- 

 belige Middelelser fra den Naturhistoriske Foresig I. Kjobenhaon, 1902, p. 386. 



6 Mem. Bos. Soc. Nat. Hist., Vol. I, p. 282. 



" Honeyman, Dr. D. Glacial Boulders of Our Fisheries and Invertebrates, Attached and 

 Detached. Trans. Nova Scotian Institute of Natural Science, Vol. VIII, Part III (1888-89), p. 

 210. 



8 Barrows, A. L. The Geologic Significance of Fossil Rock-Boring Animals (read before 

 the Palseontological Society of America). Bull. Pal. Soc. Amer., Vol. 28, 1917. 



9 Mollusca regions Arcticae Norvagise, p. 98, Christiana, 1878. 



