112 MADRAS FISHERIES BULLETIN VOL. XIV, 



these circumstances a foot for crawling is no longer needed; it 

 has been reduced to a vestige and serves merely as a support 

 for the strong horny operculum. Two genera are common in 

 Indian seas, Vermetus and Siliquaria; the former has an entire 

 tube ; the latter has a narrow slit or else a series of perforations 

 running along one side for the whole length of the gill chamber. 

 Their respective habitats further distinguish them ; Vermetus 

 cements its tube to rock boulders, Siliquaria lives commensal 

 with sponges, its coils sunk within the mass of the sponge to 

 which it gives rigidity; possibly the presence of these hard 

 tubes protects the sponge against enemies which otherwise 

 might browse upon it. As Vermetus increases in size, it vacates 

 the hindmost portion of the shell, cutting off the disused portion 

 by means of a transverse partition. This is repeated frequently 

 and so produces a series of partitioned chambers at the inner end of 

 the shell cavity. 



The reefs at extreme low water in the Gulf of Kutch are so 

 covered with the tubes of the common Worm-shell, Vermetus, that 

 barefoot walking becomes dangerous; it is also found fairly abund- 

 ant on rocky ground in the Gulf of Mannar, where also Siliquaria 

 is common. 



The SCREW-SHELLS ( Tiirritdlidae) have elegantly tapered shells 

 of the general appearance of a very elongate and slender Horn-shell. 

 They grow sometimes to a length of 4 inches. The mouth aper- 

 ture is simple and thin, without any suggestion of the thickened or 

 everted lip seen in the Horn-shells. Like Vermetus, the Screw- 

 shells find the first whorls of their shell too narrow to accommodate 

 the apex of the body as they grow larger, and have adopted the 

 same habit of partitioning off the narrow disused portions. They 

 live in moderately deep water in muddy sand. Their shells are 

 often cast upon the beach on all our coasts and are quite common 

 at Madras. The only ornamentation consists of spiral ridges ; 

 there is never any trace of tubercles or varices. T. dupUcata is a 

 common species. 



The WiNG-SHELLS iStronihidae) include some of the largest 

 of the gastropods and many most interesting species. The family 

 is an extensive one with a great range in outward appearance. 

 Three genera are common in Indian seas ; Stromhus, Ptcroccra, and 

 Rostcllaria. The first two have short conical spires, and the outer lip 



