544 



THE OCEAN WORLD. 



The thirteenth family of our Ust, Tridacnidse, contains the genus 

 Tridacna, Avith only eight species, but it contains the largest of all 

 bivalve shells. The historian of the wars of Alexander the Great 

 speaks of oysters inhabiting the Indian Ocean which were more than 

 a foot long ; these were probably Tridacna, the shells of which were 

 most likely to be seen by the Macedonian conquerors. The valves 

 of Tridacna gigas are sometimes found a yard and a half in length, 

 and weighing 500 pounds. Magnificent examples may be seen 

 in the church of Saint Sulpice, Paris, where they hold the holy 

 water. These beautiful shells were the gift of the Venetian Republic 

 vo Francis I. Under Louis XIV., the cure Languet had them 



Fig. 147. — Cardium ccstatum (Linn3eu.s\ 



l)resented to the church of Saint Sulpice, where they are used as 

 basins for holy water. Another pair are exhibited in the church of 

 Saint Eulala, at Montpelier, but much smaller in size. The shells of 

 Tridacna gigas are formed, as represented in Plate XIV., of three 

 acute angles, festooned on their edges by broad sides bristling with 

 deep white scales. The hinges have two teeth ; the ligament is 

 elongated and external. 



The animal of Tridacna is remarkable for its fine colours. 

 Tridacna serrifcra is of a beautiful blue round the edges of the mantle, 

 rayed through a shade of ver}- pale blue ; more in the interior of the 

 mantle is a row of small ocelli of a yellowish green ; the centre is a 

 bright violet, with brownish longitudinal punctured lines. "We have 

 at this moment before our eyes,"' say the travellers Quoy and 

 Gaimard, "one of the most charming spectacles that can be seen, 



