740 CLASS XII. 
Tridacna Brua. (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. TZridacna hippopus Buainv., Chama hippopus L., Hippopus maculatus 
Lam., Rumen. Amb. Rariteitk. Tab. 43, fig. o, Buatnv. Malacol. Pl. 68, 
fig. 2, GUERIN Tconogr., Mollusg. Pl. 29, fig. 7; Indian Ocean. 
Tridacna Lam. Shell gaping at the Junula, with aperture ovate. 
Foot byssiferous. 
Sp. Zridacna squamosa LaM., Rumpu. Amb. Rariteitk. Tab. 43, fig. a, Lncycl. 
méth., Vers. Pl, 236, fig.1; Indian Ocean ;—Tridacna gigas, Chama gigas L. 
(in part), Rumpu. 1. 1. fig. B, Encycl. méth., Vers. Pl. 235, fig.1. 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 bénitier for this species of shell, Linnaus 
records a shell of this kind in the Musewm Ludovice Ulrice, that weighs 
532 pounds.—In Zridacna the opening of the /unula in older individuals is 
smaller, so that the difference between Hippopus and T’ridacna is not very 
essential. 
Family XII. Cardiacea. Mantle with lobes concrete posteriorly, 
open anteriorly for the passage of foot ; two very short trachez 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 Pot) with foot falciform, very long, 
serving for jumping. 
Sp. Cardium edule L., Buatnv. Malacol. Pl. 70 bis, fig. 3, Baster Natuurk. 
'  *Vitsp. 11. bl. 76—78, Tab. virt. figs. 1—4, Pout Test. utr. Sic. 1. Tab. Xv. 
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. 
