64 



CQNCHOLOGY. 



Termlno. 

 logy. 



Valves, 



Cicatrix. 

 Beard. 



Valves. 



Base. 



margin, or the margin on the side of the beaks opposite 

 to the ligament. In this margin there is usually a 

 small depression, or lunule. The superior margin oc- 

 cupies that portion of the shell which is situated be- 

 tween the ligament and posterior margin, and is oppo- 

 site to the hinge. In some species, the valves are un- 

 connected in part ; these shells are said to have the 

 margin gaping. 



The valves of shells are divided into right and left, 

 equal and unequal, equilateral and inequilateral. If the 

 shell is placed upon its base or hinge, with the liga- 

 ment behind, then the right and left sides of the shell 

 will correspond with those of the observer. When both 

 valves agree in size and form, then they are said to be 

 equal. The length of a shell is in the direction of a line 

 drawn from the beaks to the superior margin; the breadth 

 is in the direction of a line drawn at right angles to the 

 former. When the longitudinal line divides the valves 

 into two equal parts, then the shell is said to be equila- 

 teral ; if into unequal parts, it is termed inequilateral. 



The cicatrix is a mark left on the inside of the valves, 

 at the point where the muscles adhered. 



The beard, or byssus, is a thread-like substance by 

 which certain species adhere to stones and rocks. 



Explanation of Terms used in the Description of Multi- 

 valves. 



In some of the genera, the valves are so strongly uni- 

 ted, that they seem to form one shell ; these are said to 

 be articulated. In others, a membranaceous substance, 

 termed the ligament, connects the valves together, and 

 sometimes lines the cavity of the shell. 



The base is sometimes affixed to other bodies directly, 

 or possesses an intervening tubular fleshy peduncle. The 

 accessory valves, or operculum, in some close, the prin- 

 cipal entrance like a lid ; in others, they are united to 

 the primary valves. 



Having thus noticed, in succession, the principal con- 

 chological systems which have made their appearance ; 

 and having explained a few of the terms generally used 

 in the science, we now proceed to lay before our readers 

 a system of British conchology. Had we attempted to 

 give a description of all the known species and genera 

 which have been ascertained, we would have increased 



the article to an unwarrantable length ; and to have Termino. 

 confined ourselves to the description of the genera io SY- 

 merely, would have rendered the present remarks of ^""V" 

 less general utility. We propose to give at present a 

 description of all the British species, with a few re- 

 marks illustrative of their history ; and under the arti- 

 cle Testaceology, to give an account of all the known 

 genera, with an enumeration of all the species which 

 have been referred to each genus. 

 . Instead of adopting the Linnsean arrangement, which 

 in many respects we view as defective and unnatural, 

 we have only conformed to his general divisions, pla- 

 cing the univalves, however, in the first, and the multi- 

 valves in the last division. This was the ancient me- 

 thod of distributing shells, and certainly the most obvi- 

 ous. The student of nature is, by such a method, led 

 from the examination of the more simple shells, to those 

 which are more complicated in their structure, and thus 

 pursues the plan so successfully followed in the other 

 sciences. We have judged it expedient to make a few 

 alterations in the distribution of the univalves, for the 

 purpose of bringing more closely together shells natu- 

 rally allied. Thus we have placed those univalves 

 whose cavity is entire, or unilocular, in a separate divi- 

 sion from those shells which are furnished with a many- 

 celled cavity, or which may be termed mullilocidar. 



The unilocular shells admit of a twofold division. 

 Those destitute of a columella, or pillar round which 

 the shell revolves ; and those which are furnished with 

 a columella, or pillar. This proposed arrangement, re- 

 quires the formation of a few new genera. From this 

 little confusion can arise, as we have invariably retained 

 the specific appellations by which the shells are at pre- 

 sent known, and have mentioned the genera to which 

 they formerly belonged. We have ventured to add a few 

 new species to the testacea of Britain, which have come 

 under our own inspection. Of these, drawings will be 

 given. 



When describing the several species of British shells, 

 we shall sometimes give a description of the contained 

 animal when necessary, for the purpose of specific dis- 

 tinction. Under the article Mollusca, we propose to 

 lay before our readers a description of the different inha- 

 bitants of shells, with remarks illustrating their physio- 

 logy. 



OHDER I. UNIVALVES. 



Univalves/ This division of testaceous bodies was first proposed 

 ""■"""V*"' by Aristotle, and has been more or less employed by 

 every succeeding conchologist. All those species are 

 included in this division whose shell is composed of one 

 piece, destitute of a hinge, and not furnished with any 

 accessory valves. 



The order admits of a twofold division, for the pur- 

 pose of separating the unilocular shells from those which 

 are multilocular. 



DIVISION I. UNILOCULAR. 



Unilocular ^ HE unUocluar shells were first separated from the 

 shells. multilocular species by Breynius, as appears from the 



use which he made of the terms Monothalamia and Po- 

 ly thalamia. Bose has employed, for the same purpose, the 

 terms Unilocular and Multilocular in his system. Al- 

 thoughless expressive than the termsofBreynius, they are 

 more generally understood. The shells of this division 

 have a one-celled cavity, and are more simple in their 

 formation than the multilocular testacea. They admit 



of a division into two sections ; those which are desti- Univalves. 

 tute of a pillar may be termed Astulidia, and those •— -y— I 

 which are furnished with a pillar Stulidia. 



SECT. I. ASTULIDIA. 



The shells which we include in this section, are such A3tulida. 

 as are destitute of a pillar or columella upon which they 

 are formed. Those species which are spiral, have the 

 whorls placed laterally, and do not revolve round the 

 pillar. This section we propose to divide into four fa- 

 milies, characterised by a difference in the shape of the 

 shell. These families may be denominated expanded, 

 tubular, flask-shaped, or spiral. 



Family I. EXPANDED. 



In this family the cavity of the shell is open and 

 conspicuous, and the mouth is large and spreading. It 

 was first formed by Breynius, and named Lepas, as it 

 included the Patella?, which were known to Aristotle by 

 the name of Lepas. The family contains three genera, 

 Patella, Haliotis, and Sigaretus. 



