SMITH : ON MOLLUSCA FROM TIERKA DEL FUEGO. 337 



This species is allied to Chione crassa of Q,uoy & Gaimard from New 

 Zealand, but is more compressed, and ovate, the umbones being less 

 prominent. The concentric sculpture also is hardly so strong as in 

 that species. Only a single specimen was collected. The ligament, 

 6 mm. in length, is not prominent above the valves, being situated in 

 a narrow but deep escutcheon. Besides the concentric sulci, the 

 surface exhibits excessively minute radiating striae, only visible under 

 a strong lens. The hinge consists of three teeth in each valve, the 

 central one in the left valve and the two posterior in the right being 

 somewhat bifid. 



12. Mactra Fuegiensis, n.sp. Fig. vi. 



Testa trigono-ovata, inaequilateralis, tenuis, alba, periostraco fla- 

 vescente induta, concentrice tenuiter striata, carina ab umbone ad 

 marginem posticum instructa ; margo dorsi posticus arcuatim declivis, 

 anticus seque descendens sed fere rectus ; latus anticum acute rotun- 

 datum, posticum paulo latins ; margo ventraiis late curvatus vel in 

 medio subrectus ; umbones approximati, ad apicem leviter erosi ; pagina 

 interna alba, cretacea ; cicatrices et linea pallii nitentes ; cicatrix 

 antica magna, piriformis, postica major, latior ; sinus linguoeformis, 

 subprofundus. 



Long. 51"5, alt. 37'5, diam. 21 mm. 



Hob. — San Sebastian Beach. 



This species of Mactra appears to be different from any of the 

 known forms from South Patagonia, namely, Mactra edulis, King ; 

 exalbida, Gray; Patagonica, d'Orbigny; marcida, Gould; levicardo, 

 Smith ; and Jousseaumi, Mabille & Kochebrune. It is rather like the 

 last-named species as figured by Pilsbry (Amer. Journ. Sci., 1899, 

 vol. vii, pi. i, figs. 1-3), but the umbones are less prominent, the 

 anterior end is more pointed, and the size is smaller. The epidermal 

 carina down the posterior side also tends to distinguish it. Mabille & 

 Rochebrune describe their shell as "solidula" and "intus roseo-alba," 

 whereas the present species is light and thin, and dirty- whitish within. 



The hinge is normal, but the lateral teeth are small and rather close 

 up to the cartlinals. The small external or marginal ligament is 

 divided off from the resilium by the continuation of the single 

 posterior lateral tooth of the left valve and the lower of the two of 

 the right valve. The concentric sculpture upon the umbones, in 

 fresh, unworn shells, is regular and thread-like, becoming finer as the 

 shell increases. The epidermis is very finely lamellated, and some- 

 what wrinkled down the posterior side behind the radiating ridge. 

 A second faint ridge is more or less evident down this part of the 

 valves. 



13. Darina soLENOiDES (King). 



Ilab. — San Sebastian Beach (Crawshay) ; Port Famine, Straits of 

 Magellan (King). 



The name solenoides was changed by Fischer ' to Kingi, on the 

 ground that Lamarck had already used it in the genus Lutraria, of 



1 Man. Conchyl., p. 1119. 



VUL. VI. — SEPTEMBER, 1905. 24 



