744 THE LIVING ANIMALS OF THE WORLD 



Phot, by W. SavUli-Kini, F.Z.S.] [Milf,rd-m-S,a 



A QUEENSLAND OYSTER-BANK 



Illustrating another charactcrhtic growth-phase of the Australian rock-oyster 



Of the Scallops many of 

 the larger species are highly 

 esteemed for the table. It is 

 notable of them that they can 

 progress through the water 

 in a jerky, flight-like manner 

 by the repeated flapping of 

 their opposing shells. In 

 many scallops the jewel-like 

 eyes are developed in a row 

 round the margin of the 

 mantle. 



The Bivalve Class in- 

 cludes certain representatives 

 which are held in evil repute, on account of their destructive habits. PlIOLAS and its allies 

 bore their way into solid rock, bringing about its complete disintegration. From the dreaded 

 Ship-worm, or Teredo, on the other hand, there would appear to be no description of wood 

 that can withstand its ravages. 



The Bivalve Molluscs are not without fresh-water representatives. The well-known POND- 

 and River-mussels, which form the most conspicuous examples of this group, number several 

 hundred species. While insipid and of no account for the human commissariat, many of its 

 members produce pearls of value. One such, obtained from the river Conway, in North Wales, 

 is said to occupy a place in the crown of England. 



The Chitons, or Multivalve Molluscs, invite brief notice. As the last-named title 

 implies, the shell-elements in this group are relatively numerous, consisting of eight pieces, 

 or plates, which may form contiguous transverse shelly shields that entirely cover in and 

 protect the dorsal surface of the elongate, boat-shaped body, or may be more or less isolated 

 from one another. In the former instance the animal bears some considerable resemblance to 

 a gigantic limbless wood-louse, and, like that familiar terrestrial crustacean, it is capable of 

 rolling itself into a spheroidal shape as a means of protection. None of the chitons are 

 provided with eyes in the adult state in that region of their body — namely, the head — where 

 they might be most naturally expected to e.xist. Recent scientific investigation has, however, 

 elicited the fact that in various species the respective shell-plates are studded with minute 

 eye-specks, the aggregate number of visual organs thus possessed by certain forms reaching to 

 the astonishing figures of ii,OOOor 12,000. The majority of the chitons are shallow-water, 

 rock-frequenting molluscs, which may be successfully sought by turning over stones at low 

 water. 



CHAPTER II 



LJAIP-SHELLS 



A LITTLE group of double-shelled creatures, formerly regarded as near allies of the Oysters 

 and Mussels, arc the Lamp-SHELLS. Their scientific appellation, signifying " arm-footed," 

 relates to the two spirally convoluted arm-like structures which constitute the salient 

 features in these animals. That of lamp-shells bears reference to the small circular perforation 

 near the extremity, or " beak," of the united shells, which imparts to the entire structure a 

 not altogether remote resemblance to an ancient Greek or Roman lamp with its sub-terminal 

 wick-hole. In all essential points of their organisation the lamp-shells differ so essentially 

 from ordinary bivalves that they are now generally recognised as representing an independent 

 animal class, having, as a matter of fact, a closer relationship with Worms than with Molluscs. 

 In their earlier condition certain lamp-shells are indistinguishable from larval worms; while 

 the convoluted arms of the adult animals, thickly beset with bristles and hairs, closely resemble 



