174 LECTURES ON MOLLUSCA. 



cious, rasping the flesh or sucking the juices of other mollusks, crus- 

 taceans, or zoophytes. The second group are variously organized, 

 according as they scour the shores for carrion, browse on the sea 

 weed, or are satisfied, like the bivalves, with the organic matter that 

 the sea wafts to their mouths. In each group Ave find creatures of 

 equally high organization, as e. g., the whelks and strombs; in each, 

 some very low, as Magilus and Vermetus. As a general rule, the 

 operculum in the predacious group is in concentric layers ; in the vege- 

 table-feeders, more or less spiral in its growth. 



Group Proboscidifera. (Craivlers, ivitli Retractile Proboscis.) 



All these creatures are able to swallow their snouts and their tongues. 

 They have sharp tentacles, with the eyes generally placed on knobs, 

 part way up their sides. They have thin necks; and, when not hun- 

 gry, appear very innocent, as well as graceful creatures, the dangerous 

 organs being quite concealed. Their foot is large, flat, and spread- 

 ing, more separate from the body than in the snails. But when their 

 hungry or ferocious instincts are aroused, they dart out a long trunk, 

 sometimes even longer than their shell, at the end of which are vari- 

 ous drilling teeth, so arranged that they can bore a hole, even in the 

 strongest shells, and suck out the unfortunate inhabitant. Every one 

 must have observed these accurately turned holes, especially near the 

 hinge of bivalve shells. Besides this drill-bearing trunk, they have 

 a long horny tongue, or "lingual ribbon," armed with hundreds of 

 teeth, arranged in various patterns, which differ in the various fami- 

 lies. These tongues, when at rest, lie coiled up in a cavity near the 

 stomach. They do not make such quick work with their prey as do 

 the cuttles. Fancy the condition of an unfortunate clam or mussel, 

 resting peaceably in his bivalve shield, as he hears a grating noise, 

 outside his liver, going on hour after hour, lie knows not why. At 

 last he feels the drill, and then the horny tongue, entering his vitals, 

 and he is sucked out of existence without possibility of defense! 



The shell of the Trunk-bearers may almost always be known by a 

 notch or canal at the base ; the object of which is to protect, or at any 

 rate allow the egress of the breathing pipe, which, as in the Nautilus, 

 is an open gutter formed by a lengthening and folding of the mantle. 

 In most of the tribe the trunk is drawn in base foremost; but in the 

 aberrant group of Cowries, Dr. Stimpson has observed that the tip is 

 first swallowed. In another group, of which the Cones are the type, 

 there is said to be no separate tongue ; but the teeth are inserted, in 

 two rows of organs like the sting of a bee, in the substance of the 

 trunk itself. The predacious Pectinibranchs are arranged according 

 to the form of teeth on the tongue-ribbo'n. 



Foremost in rank and beauty among the Gasteropods, stands the 



Family MuricibvE, 



or Eock-shells, in which the lingual ribbon is long and narrow, with 

 a multitude of very small teeth arranged in rows of three, (I'M,) each 

 of them with several spikes. The middle row only is fixed. In Murex 



