No. 6 (192 1 ) COMMON MOLLUSCS OF SOUTH INDIA 



183 



strong and massive, is sculptured with bold concentric ridges ; the 

 colour is white, but this is obscured by a skin of dirty yellow except 

 near the umbo, where this covering is usually worn away. The 

 ligament is internal as in Mactra. 



TheMACTRASiMactridae) are widely distributed on sandy shores 

 and become plentiful when conditions are favourable. They are 

 generally thin shelled and smooth surfaced, more or less triangu- 

 lar in outline, with deep roomy valves, whence the name mactra 

 (Latin), a kneading trough. The ligament, in the form of a trian- 

 gular pad is lodged in a deep hollow or pit within the hinge and 

 immediately under the umbo. Several typically thin-shelled 

 species are common on both the East and the West Coast. Some 

 attain quite a considerable size and may exceed two inches in 

 length (M tiiinida). Numbers of a large species affected by the 

 peculiar poisonous water that occasionally devastates shore life in 

 certain places in Malabar were seen washed ashore at Cannanore 

 in a moribund condition in 1916. The best known species is the 

 pretty little Sevalamatti {Mactra corbiciiloidcs), tinted a deep violet 



Fig. 50. Seva'amatti {Mactra corbic<'.loides). Shell and hinge plate. 



colour within, common at Pamban and the neighbourhood ; its 

 shell is distinctly trigonal in outline, usually about 30 mm. in 

 length, and with deeply concave valves which are thus able to 

 give accommodation to a body relatively much larger than is 

 contained within the shallower valves of the Kakkamatti. Its 

 colour is most distinctive, externally bluish grey with pink or 

 purplish blue colouring showing through at the umbo and usually 

 another distinctly similar colour band within the margin ; inter- 

 nally the whole surface is characteristically tinted violet. When 

 partially bleached, the colour fades to a warm pink, whence the 

 local name of Sevalamatti (red matti). 



