GASTEROPODA AND LAMELLIBRANCHIA 



The Red Sea, like every other tropical sea, is an ideal field 

 of research for the malacologist. There is an extraordinary 

 quantity and variety of empty and inhabited shells on the 

 beaches and in the sea, in the sand and between the madre- 

 poric formations. The high-water mark on the beaches is 

 bordered by a continuous line of shells of the two groups, 

 gasteropods (univalves like cowries) and lamellibranchia (bi- 

 valves like oysters) intermixed with fragments of coral and 

 madrepore. In the zones most carefully searched by us, for 

 example on the coasts of the Dahlaks, of the gasteropod 

 family we collected countless nerites, all delicately coloured. 

 They are even more common, in different species, further 

 north on the Egyptian coasts and on the island of Shadwan. 

 Nerites, together with the white moon shells, are in fact by 

 far the most common shells on the Red Sea littoral and 

 because of their smooth round shape, they are the favourite 

 *house' of the hermit-crab. We shall refer to this again in the 

 section devoted to crustaceans. The family of the conch shells 

 is well represented on these beaches. Shoals of Strombus 

 tricornis are easily found at low tide lying in shallow water 

 and covered by a thin covering of algae. Other representa- 

 tives of the same family belonging to the genus Pterocera are 

 also encountered in the same zones. They are big shells with 

 spiky extensions (varying in number, generally seven) 

 adorning in a semi-circle the shiny flesh-coloured or brown 

 lip. The biggest specimens we collected measured more than 

 thirteen inches between the extremities of the spikes at the 



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