THE THREE-HORNED STKOMB. 



367 



Whatever be its shape, it is always developed from a well-defined spot, termed the 

 nucleus, which is in many cases, but not in all, the centre of the structure. The forms of 

 this most variable plate are too numerous to be separately described, but in the course of 

 the following pages the reader will often find the operculum represented in its place on 

 the mollusc, and will be able to form a better idea of it than would be gained by mere 

 description. In many instances the operculum is only rudimentary, and in others is so 

 very small in proportion to the dimensions of the shell that it is quite incapable of closing 

 the opening. This is mostly the case with shells which have very wide-spreading mouths. 

 It is a curious fact that the operculum is developed at the same time with the shell, and 

 even within the egg this plate may be detected upon the inclosed mollusc. 



On reference to the engraving, the reader will see the animal represented as in the act 

 of walking, a feat which, on account of the small size of the foot, is not achieved with 

 much ease. In front of the foot may be seen the siphon pointing downwards to the ground, 

 and on each side of the siphon are set the footstalks, which carry the eyes at their 

 extremities and a tentacle about the centre. The colour of the Beaked Spindle-shell is 

 a pale brownish chestnut, with a slight wash of yellow. The beak, a long spiny process 

 of the shell, is edged with black, and the inside is pure white. The surface of the shell is 

 smooth, and its length is about five inches in a good specimen. 





THREE-HORNED STROMB. Strombus tricvrnis. 



BEAKED SPINDLE. Rostelldria curviroslris. 



ON the left-hand of the engraving is another shell belonging to the same family, the 

 THKEE-HOENED STEOMB, represented empty, and lying on the ground in order to show the 

 curious form of its lip. 



The Strombs form a large genus, containing about sixty species, and are found in 

 almost every warm sea. They do not appear to be deep-water lovers, being mostly found 

 on the reefs at low water, and seldom extending their range beyond ten fathoms. The 

 operculum of the Strombs is rather curious in its structure, the nucleus being set at one 

 extremity, and the operculum being made up of a succession of horny plates or scales 



