HABITS OF MOLLUSKS. 495 



entirely covers the foot, whereas in this type the foot ex- 

 tends beyond the mantle and behind it in the manner of 

 a Goniodoris. In the above-mentioned figures of the 

 Trench Naturalists, there are eight distinct branchial tufts, 

 but in this animal there are but seven, arranged in a semi- 

 circular manner around the projecting tubular fecal orifice, 

 so that in these singular Mollusks, the number of tufts 

 that constitute the branchiae seems to vary ; in the beau- 

 tiful Hexabranclms prcetextus of Ehrenberg, (Symb. Phys. 

 Mollusc. 1. 1, f. 1, 2,) the branchial tufts are six in num- 

 ber, and emerge from six distinct apertures around the 

 anal orifice, which, as in Heptabranchus, is prominent 

 and tubular. 



Tropical Assimineas seldom or never live entirely in the 

 water; they love to frequent the soft muddy banks of 

 shallow ponds in shady places, or to crawl among the 

 roots of high grass on the low swampy banks of rivers. 

 The Telescopium lives among the Mangrove-roots in 

 brackish swamps, where, in some parts of the day, the 

 water entirely recedes and leaves the mud bare. Miles of 

 muddy ground beyond the range of the sea at high-water 

 mark, and kept moistened by dull trickling rivulets, are 

 planted with thousands of the large black Telescopium, 

 with their acuminated spires sticking out of the soil, 

 while the body and head of the animal are busily engaged 

 in seeking for food beneath the surface. The Terebralia 

 of Swainson loves the water more than the Telescqpium, 

 and lives nearer the sea in shallow ponds, and still, warm 

 pools, among the tangled Mangrove-roots in the society 

 of the Q,uoyia, or Leucostoma of Swainson. The Nematura 

 inhabits very shallow water in still and half stagnant 



