136 



MADRAS FISHERIES BULLETIN 



VOL. XIV, 



Covelong and along with Turbo on the stone-strewn shoals of the 

 islands and mainland of the Ramnad and Tinnevelley districts 

 where they are occasionally eaten by the shore people. 



In habits the Purples closely resemble the Murices ; they prey 

 on other molluscs, obtaining access to the soft bodies of their 

 unfortunate victims by the same expedient of boring holes through 

 their shells; they also secrete a dull crimson fluid that was used 

 by the ancients for dyeing, Rapaiia bulbosa is another common 

 Indian species and a spiny little Sistrum is a companion of 

 Urosalpinx in its depredations on pearl-oyster brood. 



The closely allied family of Coralliophilidae comprises a curious 



group of sedentary gastropods that 

 live in coral reefs, intimately associ- 

 ated with the corals. Magilus, an 

 Indian form, is like a thin-shelled 

 Purpura when it settles down upon a 

 coral ; as the latter grows, the shell 

 becomes ever the more deeply im- 

 mersed, until, to prevent itself being 

 entombed, it changes the growth of 

 its shell from the spiral to the straight, 

 lengthening it as the coral increases 

 in thickness. As the straight section 

 lengthens, Magilus fills the hinder 

 cavity of its tube with solid material. 

 An operculum is retained. 

 The VOLUTES ( Voluti(fae) have great interest in India, for besides 

 the pretty and typical Voliita intcrpuncta of our seas, the family 

 includes the great MELON-SHELL {Mclo indica). In its youth, 

 this shell has a well-developed spire as in ordinary volutes; 

 with growth, the body of the animal increases so fast that the 

 whorl becomes so inflated and overgrown that the spire is eventu- 

 ally hidden. Strong folds are present on the columella. The 

 adult form is almost globular, and the mouth whorl so roomy that 

 in New Guinea it is commonly used by fishermen as a bailer. Our 

 Indian species grows to a length of about eight inches. 

 It is fairly numerous in 5 and 6 fathoms in Palk Bay, less nume- 

 rous on the Coromandel Coast and in the Gulf of Mannar. The 

 shell is pale reddish brown blotched with a darker shade. The 



Fig. 21. Magilus showing the larval 



form of shell (B) and the 



abnormal straight form 



assumed in adult life (A) 



(after Cooke). 



