No. 6(]92l) COMMON MOLLUSCS OF SOUTH INDIA I47 



The shell is altogether hidden ; it is a long oblong flexible 

 plate, slightly convex. 



The important group of Naked-gilled Molluscs or NUDIBRANCHS 

 is not well represented on tlie Madras littoral as their especial 

 habitat is among weed-grown rocks ; there are certainly many and 

 beautiful forms but they are cither small and inconspicuous or else 

 comparatively rare. They are slug-like animals without shell of 

 any sort, and true gills are absent, their place being taken by 

 outgrowths from the back, protean in the variety of their form, and 

 often exceedingly elegant and brightly coloured. In some these 

 form rosettes, in others richly arborescent filaments, in other club- 

 shaped knobs, or even simple folds not unlike those of Lobiger. 



In certain cases the brilliant hues are assumed as warning 

 colouration- possible enemies are told to beware of the spicules 

 present in the skin or of the stinging cells which in some species 

 {Acolis for example) are developed in the dorsal processes; in 

 another class the colouring is protective and mimetic, harmonizing 

 with that of the sea-weeds and animals amid which they live. 



The rough yellowish SEA-LEMON, Doris, lives largely on 

 sponges, while the little Doto, with club-shaped appendages, feeds on 

 zoophytes. A very peculiar form is the soft gelatinous Mclibe, not 

 uncommon on the pearl-banks, which has six pairs of large semi- 

 transparent lobes upon the back, mottled olive green and brown ; 

 these drop off at a touch and when taken in a net, separate from 

 the animal, are very puzzling to one who is not acquainted with 

 Melibe. Some of the colouring within the skin is due to lowly 

 algse living in virtual partnership — symbiotic as this habit is termed. 



Study of our Indian Nudibranchs is much wanted, and offers a 

 wide field for original research ; we know almost nothing of the 

 life appearance of many species and still less of their habits. 



The origin of the group is clearly shown by the larvae which 

 possess minute nautiloid shells, furnished with an operculum, both 

 of which are cast off before the adult form is assumed. 



Order 2.— Pulmonata. 



With the exception of certain fresh-water forms which have 

 re-acquired gill-like breathing organs, the Pulmonata are air- 

 breathers in which the walls of the mantle cavity are traversed 

 by a net-work of fine blood-vessels, constituting a true lung. Their 



