231 



ISOCARDIA. 



ISOETES. 



282 



of the umbo, serve to distinguish it from the other Carditce of Bru- 

 guiere. M. De Blainville, \inder the name of hocardium, inserts it 

 between Tridacna, and Trigonia among his Camace'es. M. Rang retains 

 it in the same family, but restores Lamarck's original termination of 

 the name, and places it between Caprina and Tridacna. 



M. Deshayes, in his edition of Lamarck, remarks that the Isocardia! 

 have in truth large and contorted umbones like Chama and Oicerat, 

 but that they are regular and always free, while the true Chamce are 

 adherent and irregular. From the Carditce, he observes, they are to be 

 distinguished, both as respects the shell and the animal. In Cardita 

 the lobes of the mantle are separated throughout their length, and 

 are without siphons. In Isocardia the lobes of the mantle are united 

 posteriorly, and provided with two short siphons, or rather perfora- 

 tions, which may be compared with those of the C'ardia. Here 

 doubtless, says M. Deshayes, the Iiocardice approach the Cardlce; 

 but when the foot and the form of the branchiae in these two genera 

 are compared, the distinction is obvious. In the Cardia [COXCHACEA], 

 the foot is cylindraceous, very long, and bent hi an elbow-like form in 

 the middle ; in the Isocardice, on the contrary, it is flat, subquad- 

 rangular. and rather short. 



Isocardia has the following characters : Animal more or less 

 globular, having the borders of the mantle fringed with very fine 

 tentacular papilla:, leaving a rather large opening between them at 

 the lower part, and united posteriorly by a transverse delicate band, 

 pierced with two orifices surrounded by papillae, one for the vent, 

 and the other, lower, for respiration; foot of moderate size and 

 trenchant. 



Shell sometimes with an epidermis, very convex, globulose, heart- 

 shaped, equivalve, inequilateral ; umbones divaricated, and widely 

 divergent, curved forwards and outwards, and slightly spiral ; hinge 

 composed of two flattened hinge-teeth; ligament external, forked 

 at one of its extremities ; muscular impressions very distant. 



/. Cor, the Heart-Shell, has been taken on the British coasts. 



The llev. James Bulwer, from whose figure in the ' Zoological 

 Journal," vol. ii., the two figures below are taken, saw the animal 

 when in sea-water, and in the position represented at No. 1. The 

 feelers, or ciliated fringe of the upper orifice (the largest) of the 

 mantle, moved slowly, as if in search of food. Having remained in 

 this situation about ten minutes, water was ejected with considerable 

 force from the lower orifice, which had till then remained motionless. 

 The expulsion of the water appeared to be effected by a sudden con- 

 traction of the muscles, because this was never done without the 

 valves nearly closing at the same instant. After a few seconds the 

 valves gradually returned to their open position, and remained quies- 

 cent as before, till the water was again ejected with a jerk; this 

 alternating process was repeated during the whole time his specimens 

 (which were trawled up in very deep water on the east coast of 

 Ireland) were under his examination, but at shorter intervals on 

 receiving fresh supplies of sea-water. The animal appeared to Mr. 

 Bulwer to be insensible both to sound and light, as the presence or 

 absence of either did not at all interrupt it* movements ; but its 

 sense of feeling appeared to be very delicate. Minute subst.-incea 





Heart-Shell (Iiocardia Cur). 



l t ralvrs open, to show the animal and the fcdcr* or, ciliated fringe of the 

 upper and lower orifices ; 2, one of the valves, showing the animal with its 

 ibarp-eUgcd foot and the muscular impressions. 



dropped into the orifice of the mautle instantly excited the animal, 

 and a column of water strongly directed expelled them from the 

 shell; with so much strength was the water in some instances ejected, 

 that it rose above the surface of three inches of superincumbent 

 fluid. (' Zool. Jour.,' vol. ii.) 



Shell of laocai dia Cor, valves closed. 



Lamarck recorded four species, including Isocardia scmimlcata. 

 M. Deshayes, in his edition of that author, adds four others, reckoning 

 that species : making eight in all, recent and fossil. 



The species are found in the European and East Indian seas, and 

 those of Australia. They have been dredged up from mud and sand 

 at depths ranging from 10 to 20 fathoms. 



Fossil Isocardue. 



Mr. G. B. Sowerby remarks ('Genera of Recent and Fossil Shells') 

 that several fossil species are given in plate 295 of Sowerby's ' Mineral 

 Conchology,' one of which is from the London Clay, and the other 

 from Kelloway's. Mr. Q. B. Sowerby, in a note, states that a fossil 

 species also occurs in the Crag, which so nearly resembles the /. Cor 

 that he knows not wherein the specific difference consists ; and, in 

 the text, goes on to state that according to Brocchi (' Conch. Foss. 

 Subap.,' ii. 520), two varieties of I. Cor are found in a fossil state in 

 several parts of Italy ; but as a subject upon which much diversity 

 of opinion exists is here brought iuto question, he would recommend 

 an attentive and comparative re-examination of the fossil with recent 

 specimens, before the inquirer comes to an absolute decision upon 

 this point. Another fossil species, he observes, is found at Piacenza, 

 namely, /. arietina, Lam. ; and he has figured I. Basochiana (Defr., 

 'Diet, des Sciences Naturelles'), a new species found by M. DeBasoches 

 de Falaise, in the district of Coutances. He thus concludes his remarks 

 upon the fossil species of this genus : " We think we may venture to 

 express our opinion that all the fossil specimens published in various 

 books, and existing in various collections, are not distinctly charac- 

 terised Isocardia?, but only the casts of the insides of othep bivalves : 

 the best distinguishing character is in the groove formed for the 

 extension of the ligament from the hinge to the umbo. It is 

 incumbent on us to mention that in Isocardia the line to which the 

 mantle is attached, passing from one muscular impression to the 

 other, is entire." 



M. Deshayes, in his Tables, records two living species and three fossil 

 (tertiary) ; and /. Cor as both living and fossil (tertiary). 



Mr. Lea places his genus Hijipayue (of which he gives an engraving) 

 under the family Cardiacea. (' Contributions to Geology,' 8vo., 

 Philadelphia, 1833.) He states that he has in vain endeavoured to 

 place this shell in one of the established genera. In its general 

 character he says that it approaches most closely to the /. Cor, but 

 that it cannot be plaeed in that genus, being destitute of teeth. 

 It bears, he adds, some resemblance to the genus Inoceramw ; but, 

 he continues, the hinge, in that genus " closes by a series of oblong 

 fossete," and besides it is very inequivalve. In its natural order he 

 thinks that it seems to follow the genus Isocardia, and he proposes 

 to place it in that position. JJi/jprigns occurs iu the Claibome beds 

 (tertiary of Alabama Eocene of Lydl). 



Other species of Isocardia have Veil found from the Oolitic beds 

 upwards, but they resemble more closely tropical species than 

 1. Cor. 



1SOCRINITES, a genus of Crinoidea. (Goldfu=s.) 



I'SOETES (from laos, equal, and (TOS, year), a Cryptogamic genus 

 of Plants belonging to the natural order LycopodiaceiF. The capsule 

 of the plant does not open, and the fructification is inclosed within 

 the swollen base of tke leaves ; it has sponiles of two kinds, which 

 are attached to filiform receptacles. The organs of fructification in 



