﻿174 Transactions. — Zoology. 



one next in front ; these valves are inserted into a tough ligament called the 

 mantle, which holds them all together, and which expands into a broad margin 

 I'ound the aninial. (PL IX.) The margin of the mantle presents many differ- 

 ences, whichare used to divide the family into various genera. Sometimes it is 

 covered with small imbricated scales, sometimes with spines, while in many 

 species it is nearly smooth, or tomentose with short hairs. The anterior and 

 posterior valves are smaller than the others, and generally rounded on the out- 

 side margins ; the intermediate ones are broader than long, and elevated in the 

 centre, either by being uniformly arched, or by each side being more or less 

 flattened so as to form two sides of a triangle. These intermediate valves are 

 usually divided into a dorsal, or median, area, and a triangular lateral area on 

 each side, which are called respectively the median and lateral areas. The 

 sculpturing on the lateral areas is generally different from that on the median 

 areas, while it is almost always the same as that on the anterior and posterior 

 valves, or terminal areas. 



The animal is of an oval or oblong shape, with a long and broad foot rounded 

 at each end. The head is not furnished with eyes nor with tentacles, but has 

 a waved membranous hood surrounding the mouth. The tongue is long, 

 spirally rolled, and armed with hooked horny teeth. The branchiae, or 

 breathing organs, are in the form of a series of small triangular leaves, and are 

 situated in a row on each side of the body, between the mantle and the foot. 

 The sexes are distinct. They adhere to rocks, or shells, sometimes even to fish, 

 and when detached roll themselves up ; a few are found creeping on sand. 

 They generally live between high and low water marks, biit some small species 

 inhabit the sea to a depth of twenty-five fathoms. Some fix themselves on the 

 upper surfaces of rocks, and, when the tide is out, bear the full heat of a tropical 

 sun on their backs, while others are only to be found during very low tides, 

 and are seldom exposed to the air. The greater number, however, inhabit the 

 bottoms of rock-pools, or the under surfaces of stones, and so always keep 

 moist even when the tide is out. 



Very little is known about their habits further than that when covered 

 with water they move slowly from place to place in quest of food, which is 

 supposed to be entirely vegetable. 



They adhere to the rocks with great tenacity, and in order to collect them 

 without bi-eaking the shell they must be taken by surprise, the blade of a knife 

 being slipped suddenly under them and one side lifted up. If the animal is at 

 once removed from the shell the mantle contracts, and cannot be straightened 

 out again without great risk of breaking or displacing the valves. The best 

 method of proceeding is to place the animals, immediately after they have been 

 collected, on small flat stones, or pieces of slate, under the water, when they 

 will soon attach themselves, and may then be removed, and the stones, with 



