740 CLASS XII. 



Tridacna BRUG. (Species of Chama L.). Shell transverse, 

 inequilateral. Points approximate. Hinge with two teeth, placed 

 behind the points under the ligament ; the posterior in the right 

 valve bipartite, a groove receiving the posterior tooth of the left 

 valve. 



Hippopus LAM., lunula closed. Foot not byssiferous. 



Sp. Tridacna hippopus BLAINV., Chama hippopus L., Hippopus maculatus 

 LAM., KUMPH. Amb. Rariteitlc. Tab. 43, fig. c, BLAINV. Malacol. PI. 68, 

 fig. 2, GUEBIN Iconogr., Mollusq. PI. 29, fig. 7 ; Indian Ocean. 



Tridacna LAM. Shell gaping at the lunula, with aperture ovate. 

 Foot byssiferous. 



Sp. Tridacna squamosa LAM., KUMPH. Amb. Rariteitk. Tab. 43, fig. A, Encyd. 

 me'th., Vers. PI. 236, fig. i; Indian Ocean; Tridacna gigas, Chama gigas L. 

 (in part), HUMPH. 1. 1. fig. B, Encyd. meth., Vers. PI. 235, fig. i. This species 

 also occurs in the Indian Ocean ; it is the largest conchifer known. For- 

 merly it was the custom to ornament gardens with them as basins of foun- 

 tains ; in churches these shells sometimes serve for holding the holy- water, 

 as two very large ones may be seen in St Sulpice at Paris; hence the 

 derivation of the French name benitier for this species of shell. LINNAEUS 

 records a shell of this kind in the Museum Ludovicce Ulricce, that weighs 

 532 pounds. In Tridacna the opening of the lunula in older individuals is 

 smaller, so that the difference between Hippopus and Tridacna is not very 

 essential. 



Family XII. Cardiacea. Mantle with lobes concrete posteriorly, 

 open anteriorly for the passage of foot ; two very short tracheae dis- 

 tinct, foraminiform, with margin girdled by cirri. Foot large, falci- 

 form, not byssiferous. Ligament external. Shell regular, equivalve, 

 free. Hinge with two teeth under the point, receiving each 

 other by mutual insertion, and one or two lateral. Two muscular 

 impressions remote. 



Cardium L. Shell subequilateral, shorter posteriorly, more 

 gibbous anteriorly, mostly furnished with longitudinal ribs. Four 

 teeth in each valve ; with two oblique under the points, receiving 

 each other crosswise by mutual insertion, and two lateral remote, 

 compressed. Animal ( Cerastes POLI) with foot falciform, very long, 

 serving for jumping. 



Sp. Cardium cdule L., BLAINV. Malacol. PL 70 bis, fig. 3, BASTER Natuurk. 

 Uitsp. II. bl. 76 78, Tab. vm. figs, i 4, POLI Test. utr. Sic. i. Tab. xvn. 

 figs. 13 15; on the shore in the North and Mediter. Seas; this bivalve, 

 like some other species of this genus, is used for food ; the common name 

 in Zealand is kokhaan. 



