748 CLASS xn. 



Tellinides LAM. Posterior margin of shell without irregular 

 fold. 



Sp. Tellina Timorensis BLAINV., Tellinides Timoriensis LAM., BLAINV. Mala- 

 col. PL 72, fig. 2. (DESHATES has rejected this sub-genus, calling to mind 

 that some Tellince by slow degrees conduct to this form. 



Fragilia DESH. Shell subtrigonal, gibbous, anteriorly rotun- 

 date, posteriorly longer. Hinge with two teeth diverging in each 

 valve. 



Sp. Tellina fragilis L., Petricola ochroleuca LAM., POLI Test. utr. Sic. i. Tab. 

 XV. figs. 22, 24, DESH. Conchyliol. PL 12, figs. 13 25. Hab. in Medi- 

 terranean. 



Family XVIII. Mactracea. Mantle open anteriorly, concrete 

 posteriorly, produced into two tracheae, in some separate, in others 

 coalesced. Foot compressed, triangular. Shell equivalve, free. 

 Ligament internal, received in a pit ; in some an external ligament 

 as well as an internal. Two muscular impressions remote. Im- 

 pression of mantle marked posteriorly with a sinus, in some broad, 

 in others deep, narrower. 



Amphidesma LAM. (in part), KECLUZ, DESH. Shell rotundate, 

 suborbiculate, thin. Hinge with two teeth in each valve. Liga- 

 ment double; external short; internal in a pit of hinge oblique, 

 deep, narrow. 



Sp. Amphidesma variegata LAM., Encycl. meth., Vers. PI. 291, fig. 3; Indian 

 Ocean; Amph. solida GRAY, DESH. Conchyliol. PL n, figs. 10 12, 

 South Sea, at the coast of Peru. 



Syndosmya KECLUZ, DESH. Shell transverse, oval, thin, with 

 anterior side shorter. Hinge with two teeth in right valve, with 

 intermediate foveola receiving the single tooth of left valve. Two 

 lateral teeth. Ligament double ; external small, internal received 

 in a spoon-shaped process. Animal with two tracheaa long, 

 separate. 



Sp. Syndosmya alba, Amphidesma Boysii LAM., DESH. Conchyl. PL 8 bis, 

 figs. 6 8, &c. 



Trigonella DA COSTA, DESH. (Species of Mactra GMEL., sub- 

 genus of Mactra Cuv., spec, of Lutraria LAM.) Shell orbiculato- 

 trigonal, flat, subequilateral, with anterior side shorter, rotundate, 

 posterior subhiant. Hinge narrow, with two small teeth in right 



