THE RESULTS of DEEP-SEA INVESTIGATION in the 

 TASMAN SEA. 



3. MOLLUSCA FROM ElGHTY FaTHOMS OFF NaRRABEEN. 



By C. Hedley, Conchologist. 

 (Plates liv.-lvi.) 



The fourth collection from the continental shelf of this coast 

 I have been privileged to examine was discussed in the last 

 issue of this serial. The fifth forms the subject of the present 

 article. It was obtained under the circumstances above related, 

 on 7th June, 1906, in a single haul of the bucket dredge in 

 eighty fathoms, twenty-two miles east of Narrabeen, New South 

 Wales. 



Probably the alluvial of the Hawkesbury River is here spread 

 by the prevailing current, for at this point the continental shelf 

 extends in an unusually broad terrace. A depth of two hundred 

 and fifty fathoms is attained at the same distance east of Botany 

 Heads, while six hundred fathoms are reached south of UUaduIla 

 at no greater distance off tlie land. 



According to the " Challenger " observations, long continued 

 west winds push the great warm current beyond this station, but 

 usually its stream sweeps over the position. A ricli fauiui in- 

 habits this spot. In all I have separated two hundred and forty 

 species of shells, a total far greater than was realised by the best 

 liaul of the voyage of the " Challenger." This result is partly due to 

 the productive nature of the ground, and partly to the efficiency 

 of the bucket dredge as a collecting tool. 



Assuming that we have here the entire molluscan fauna of 

 three square feet of the sea floor, it is interesting to speculate 

 what proportion of a fauna extending over thousands of square 

 miles of continental shelf, subsists on three square feet. If we 

 counted the plants of three square feet on a river bank, what pro- 

 portion would they represent of the total flora of the valley ? I 

 am inclined to suppose that the cases are not parallel, that a 

 scjuare foot of the sea floor contains a lai'ger proportion of the 

 fauna of a square mile than happens on land. This is supported 

 by the continuity of fossil zones elaborated by modern palaeon- 

 tologists, and is deducible from the uniformity of conditions in 



