716 CONTRACTILITY. 



Tliis tabular view of the classification exhibits macea, but underneath them. The family of 



certain particulars, upon which we deem it the Ostracea we now believe to consist of the 



necessary to offer a few explanatory remarks, single genus Ostrea, and we propose under the 



As we said before, the series as a whole may name of Placunidte a family containing the 



be regarded as a common trunk, from which three genera Placuna, Placunonomia, and Ano- 



various branches spring, sometimes anastomo- mia, which according to our views constitute a 



sing, sometimes ending abruptly. It is thus descending and lateral line really intermediate 



that from the Clavigella we observe a lateral line to the Conchifera and the Brachiopoda. 

 departing, formed of the genera Fistulana, 



Ga/eomma, and those of Lamarck's family BIBLIOGRAPHY. - The folding works 



r j . ii i / essays may be referred to as still interesting 



of Petncola. These genera descend parallel to on t j he na jf aral history of the Conchifera. Reau- 



the common trunk of the classification, so as mur, De la formation et de 1'accroissement 



to approximate in as great a degree as possible des coqnilles, Acad. de Paris, An 1709 et An 



the genus Venerupis to the genus Venus. The * 71 6 ; Ej. De la maniere dont pluieon cspeces 



genus Pandora has numerous analogies on one t^SI^ ^'i SSSfv^ 'w^ST^a 



. , . , /-ii &c. ibid, An 1711. Walch, Vom Wachsthum und 



side with the Corbula, but it has also many den Farben der Konchilienschaalen. Besch. der 



with the members of the genus Osteodesma, on Berlin. Naturforsch. Gesell. B. i. S. 230. Mittler, 



which account it is made to depart laterally Anmerk. ueber Walch, ibid, B. ii. S. 116. * 



from the Corbula, and to ascend towards the Owner, Nouvelles Rech. sur les coquilles bivalves, 



Osteodesmata. The Lutraria are also variously s ci . 6t6 ? h Sf >Bia % ^' 7 ' T P " ' v T'^T**^!? 



/TV / j. of the Scallop, Philos. Trans. Year 1697. Ant* 



related to several genera of the Osteodesmata, mn der Hei / gf Anatome M ytuli, 12mo. Amst. 



and this genus is joined to that of the Thracia 1684. Bojanus, Sendschreiben an G. Cuvier 



by means of the genus Anatinella, which we iiber d. Athmen und Kreislaufswerkzeuge d. Zwei- 



place crosswise to connect the genera just men- shaaligen Muscheln, 4to. Jena, 1820. Mangili, 



tioned. In the Mactracea, we pass without ^ icei : che . nu vi zootoroiche sopra alcune specie di 



, ,. "7 ,1 Conchiglie Bivalvi, 8vo. Milano, 1804. Brack, 



any very great stride from the Lutraria to the De ovi s ostreorum , Misc . Ac . Nat . cur . Dec . 2, 



Mactra, from the Mactra to the Erycma An 8. Koehlreuter, Obs. anat. physiol. Mytili 



and to the Amphidesma. Farther, in order cygnei (Lin.) concernentes, Nov. Act. Petrop. 



not to interrupt this series of relation- t vi. 



ships, we place upon a lateral line departing (G. P. Des Hayes.) 



from the Mactra the two genera Mesodesma 



and Crassatella. Every naturalist knows how CONTRACTILITY. Since it has been 

 great the resemblance is between the flat and generally understood, that all the most striking 

 broad Solens ( Soletellina, De Blainv.) and the and conspicuous movements which take place 

 PsammobifK ; but we also know that the genus in living animals, depend on peculiar contrac- 

 Psammobia has so many analogies with the tions of certain of their solids, the circum- 

 family of the Tellinida, that it is impossible to stances of these contractions, the causes by 

 detach it from this family in order to include it which they are excited, and the laws by which 

 within the family of the Solenaceae. To avoid they are regulated, have been justly regarded 

 interrupting the relations of this genus to those as objects of the highest interest, and of fun- 

 of the Solen family, we have recourse to an damental importance, in physiology. The 

 ascending line composed of the genera Solen- term Irritability was employed by Haller and 

 ertus, Panoptea, Solen, Solemya, and Glyci- his followers, to denote all such contractions 

 meris, by which means we approximate, as in living bodies, as they judged to be peculiar 

 much as possible, these last genera to the fa- to the living state ; but more recent inquiries 

 milies Pholadia and Osteodesmata, with which have shewn the necessity of distinguishing 

 they have in fact unequivocal relationships in different species of these contractions ; and the 

 point of organization. We consider the family more comprehensive term Contractility is now 

 of the LucinidtE as a lateral and truncated pretty generally employed. To this the epithet 

 branch of the Conchidte, divaricating from the Vital, in physiological discussions, may usually 

 genus Astarte. With regard to the Cyclada, we be understood as prefixed, 

 place the genus Glaucoma of Mr. Gray laterally, It is to be remembered, however, that several 

 between the Cyrenas and the Venuses, so as to of the animal textures are endowed with a pro 

 establish the connexion between the two ge- perty of contraction, in certain circumstances, 

 nera; whilst departing also from the genus which is not peculiar to their living state, but 

 Cyrena we place our genus Cyrenella obliquely subsists as long as their structure remains unal- 

 in order to make it join that of Lutina, tered after death ; and the distinction between 

 this genus of Cyrenella being to Cyrena the phenomena resulting from this cause, and 

 and Lucina that precisely which the genus those which are strictly vital, has not always 

 Glaucoma is to Cyrena and Venus. To been accurately observed. Thus many of the 

 us the family of the Chamacea is a lateral soft animal textures, muscles to a certain de- 

 offset from that of the Cardiacea, and although gree, tendons and ligaments in a greater degree, 

 the Etkerue and the family of the Rudistes are and arteries in a still greater degree, are elastic, 

 in reality among the number of those Conchife- and liable to contractions from that cause when 

 rous mollusca which have the lobes of the stretched. The Contractilite de Tissu of Bichat 

 mantle disjoined, still as they do not imme- is in most cases to be considered simply as 

 diately arrange themselves in any particular Elasticity, although in some cases (as when he 

 part of this section, we have placed them to the assigns this property as the reason of the re- 

 side in continuation of the family of the Cha- traction of the cut extremities of a living muscle 



