196 LECTURES ON MOLLUSCA. 



creature folds its foot round the Gorgonias on which it lives, carrying 

 its shuttle gracefully over its head, the edges of the lip and canal being 

 elegantly adorned with tufts. In other species the canals become 

 shorter and shorter till they are only a prolonged notch. The smaller 

 forms are colored differently, in the same species, according to the 

 coral on which they feed. In Simnia, the outer lip is quite sharp, 

 and the animal has a long foot and breathing pipe, as in Trivia. None 

 of the Cowry or Shuttle tribe have any operculum. 



Sub-order ROSTRIFERA. {Muzzle Bearers.) 



The remainder of the Comb-gilled Crawlers have a longer or shorter 

 snout which is not retractile, and is technically called a rostrum. In 

 the Strombs and their allies, the snout is very long, and the teeth are 

 adapted for tearing carrion, on which they live ; but in most of the 

 families, they browseupon the herbage. The proboscis-bearing shells 

 are all from the seas or estuaries ; but the vegetarian tribes are also 

 found in fresh waters or on land. In the latter case, the gill cavity is 

 changed into a lung. The teeth of the Rostrifers are always in seven 

 series, 3 • 1 • 3 : but in the first group the lateral teeth are claw shaped, 

 as in Cassis and Natica : while in the Periwinkle group they simply 

 have serrated, edges, adapted for rasping plants. The Rostrifers are 

 arranged by Dr. Gray according (1) to the shape of the foot, (2) to the 

 position of the eyes, and (3) the shape of the gills. The dentition has 

 not been regarded by him of primary importance, as in the trunk- 

 bearers. It is impossible to group them in a straight line so as to 

 show all their known affinities ; a few families, as the Strombs, Worm- 

 shells and Apple-snails, appearing to disturb every natural order of 

 succession. 



First Group. Teeth arranged as for animal food,. 



Family Strombid^i. {Wing Shells.) 



The Strombs and their allies are very strange creatures. They are 

 rather leapers than crawlers, and jump about the shore, using their 

 foot as a leaping pole, searching for dead fish and other refuse, of 

 which they are the useful scavengers. The shape of their body is 

 altered to suit their change of habits. As they stretch themselves out 

 of the shell, the body seems made up of scraggy limbs, like a dead tree 

 partially deprived of its branches. The foot, which is a stout, muscu- 

 lar lever, is the trunk of the tree : from this branches off the head, if 

 indeed you can say that there is any distinct head or neck ; for it con- 

 sists, first of a stout truncated branch, which is the long muzzle with 

 the mouth at the end ; next of two smaller branches, also truncated at 

 the end ; these appear to be tentacles, but are really stout pillars for 

 the eyes to rest in ; lastly, of the true tentacles, which are little pointed 

 twigs growing out of the eye-stalks. The second great branch is an 

 arm going off at right angles to carry the operculum. This is long, 

 claw-shaped, and toothed at the edge, only attached to the animal by 



