TRID ACN A. 



Plate II. 



Species 1. (Fig. h, c, Mus. Cuming.) 



Tlie shells here figured represent the great T. gigas in 

 an early stage of growth. At first. Fig. 1 1), the scales are 

 lofty, very regular, and neatly-defined. Presently they 

 become eroded and worn down, whUst the successive ad- 

 ditions of scales, as shown at Fig. 1 c, are shorter and 

 closer set. Lastly, as in the specimen represented in 

 Plate I., the development of the scales is reduced to a 

 mere crowded incrustation of rude layers of growth. 



Species 3. (Fig. a, b, Mus. Cumiug.) 



Trii).\cna elongata. Trid. testa ovato-oblongd, antice 

 elpngato-prodactd, qiiliique- ad sex-costatd, costis coa- 

 vexii, regulariter tt subcoxfertiin squamatis, iiittr- 



stiliis inter codas biliralis, inter squamas lavibiis ; 

 alba vel citrind. 



The elongated Tridacna. Shell ovately oblong, an- 

 teriorly elongately produced, five- to six-ribbed, ribs 

 convex, regularly and rather closely scaled, interstices 

 between the ribs two-ridged, between the scales 

 smooth ; white or lemon-yellow. 



Lamarck, Anim. sans vert. vol. vii. p. 9. 



Hab. PhQippine Islands; Cuming. 



The elougately-produced growth of this species gives 

 a peculiarly gibbous form to the shell ; and it retains this 

 characteristic contour in all stages. In the British ilu- 

 seum there is a specimen of quite colossal dimensions, of 

 precisely the same form. The scales are very regularly set 

 throughout the ribs in neatly-defined fm-belows. 



June, 1863. 



