146 



HARDWICKE'S SCIENCE-GOSSIP. 



similar to Patella, namely, Fissurella, our native 

 representative of which, the Keyhole Limpet 

 {Fissurella reticulata), although not so abun- 

 dant as the former, yet is by no means a rare shell. 

 In this species we have an opening on the apex, 

 through which the water that has passed through 

 the system flows. The third, the genus Punctinella, 

 as exemplified by our Perforated Limpet {Punctinella 

 noachina), has the opening just in front of the 

 apex. The fourth of our series is the genus Rimula, 

 of which we have no British example, this shell 

 being confined to the Philippines, and having its 

 opening midway between the apex and base. We 

 possess, however, the fifth, which is the genus 

 Emarginula, in. the Notched Limpet {Emarginula 



parts contained within the shell, its outer edge 

 being thickened into a glandular collar, from which 

 the increase in the shell's size arises. When the 

 animal desires to enlarge its dwelling, it carefully 

 fastens this collar all round the edge of the shelL 

 The glands in this collar, which secrete calcareous 

 matter, then deposit it, layer upon layer, on the 

 edges ; and thus the shell is enlarged. The shape 

 also of the shell depends on this mantle, those 

 animals which have spiuous or ridged shells having 

 corresponding furrows and depressions in it. 

 There are also glands in the collars of the mantle 

 which secrete colouring matter, which affects 

 accordingly the tint of the shell. The rest of the 

 mantle, tliat is, all but the collar, is destitute of 



Fig. 86. Ormer Shell {Haliotis tuberculata). 



reticulata), where the opening is at the base ; 

 and the sixth is the subject of this article, the 

 Ormer, or, as we might more especially call it, the 

 Ormer Limpet (Ilalioiis tuberculata), completing 

 the series. In it we have the openings extending 

 from the apex to the base. Guernsey is the 

 northernmost spot in which the genus Haliotis is 

 found, and it is a fact worthy of notice that speci- 

 mens of the Ormer from that place are, as a rule> 

 much larger than those from the Mediterranean 

 Sea and other places in the Lusitanian province 

 ■which it inhabits. Having now made a short 

 survey of the shell, we will pass on to its inhabitant. 

 Reference to the illustration, which represents the 

 animal in the act of moving along, shows us that, 

 like the common garden slug {Limax agrestis), it 

 moves along on a broad fleshy disk situated beneath 

 the body. This is called the ventral disk, and on 

 it, a little elevated from it, is a smaller one, having 

 a rough ajjpearance, and studded here and there 

 with some curious-looking spikes. Conchologists 

 term this the mantle, as it in some places overlaps 

 the shell. This mantle covers the whole of the 



these glands ; and so the deposits from it are not 

 coloured, but layers of a pearly substance are laid 

 down. This forms the iridescent opaline sub- 

 stance so extensively used in decorations under the 

 name of Mother-of-Pearl. What the ofiice of the 

 spikes may be, I am rather at a loss to determine, 

 unless they help to prevent the approach of foes 

 near the soft parts of the animal. I am tlie more 

 inclined to take this view, as similar spines project 

 from the apertures, where any predacious miirex 

 might easily insert its poison but for this provision. 

 The head is furnished with four tentacles, the upper 

 pair being longer and more slender. These act as 

 feelers, a most delicate sense of touch being placed 

 in them : they can be drawn inside the shell at 

 leisure, folding inside out, as we pull off a stocking. 

 When not moving, the whole animal is drawn 

 within the shell, clinging fast to the rock. 



The economical value of this species and its foreign 

 congeners is very great. They are collected by the 

 fishermen, who go out in boats at spring tides, and, 

 after collecting them from the rocks, take their 

 haul to the market. Before, however, being, fit for 



