Invertebrate Gallery of the Indian Museum, 143 



which are often of great length. The siphons are retrac- 

 tile, and when retracted are lodged in the deep inflexion 

 known as the pallial sinus (see the prepared shell of 

 Hiatula in Case 172A). 



The shell is usually thick and solid, but is sometimes 

 as in the species of Tellina, thin and delicate. 



The Veneracea are of world-wide distribution, and the 

 great majority of the species are marine, although a 

 few are found in the brackish waters of estuaries. For 

 the most part they live buried in sand or mud in shallow 

 water ; but a few species bore into solid rock. 



2nd Family Myacea, [Cases 176 B,C — 177A]. ' 



The typical forms of this family are known as 

 " Gapers ", from the fact that the valves of the shell gape 

 even when fully adducted. The lobes of the mantle are 

 united throughout, except for a small chink in front for 

 the passage of the foot. The siphons are generally large 

 and long and are very often bound together along more or 

 less of their extent and enclosed in a common envelope of 

 skin. In many cases the gills are prolonged into the in- 

 current siphon. The hinge-teeth of the valves in this 

 Family are often ill developed. The Myacea are for the 

 most part marine, but a few are estuarine and fluviatile. 

 Their usual mode of life is deeply embedded in sand or 

 mud with the ends of the siphons protruding from between 

 the gaping valves of the shell : some species, however, bore 

 into rock. 



3rd Family Pholadacea, [Case 177 B, C]. 



This family includes the universally distributed Pholads 

 and Shipworms, that work such damage to piers and 

 breakwaters, into which, whether wood or stone, they bur- 

 row in swarms. The long cylindrical burrows in which 

 the Shipworms live are more or less completely lined with 

 carbonate of lime, and form shelly protective tubes in which 

 the true shell lies ; and in Aspergillum the true shell itself 

 becomes incorporated with the protective tube, the two 



