60 THE VOYAGE OF H.M.S. CHALLENGER. 



more suddenly sloping. The lower outline is very gently curved, rising rather higher 

 in front than behind. The beaks are small, brown at the tips, placed a little behind the 

 centre, and raised a trifle above the hinge-line. The hinge-plate and the teeth, including 

 the slender laterals, are white. The interior is somewhat glossy, of the same colour as 

 the exterior, showing a pallial sinus, sharply rounded at the end, and reaching a little more 

 than a third of the length across the valves. 



Length 15 mm., height 10, diameter 7. 



Ilahitat. — Admiralty Islands, north-east of New Guinea, in 16 to 25 fathoms. 



The single specimen under examination may not represent the adult state of this 

 species ; but, judging from its general appearance and the somewhat thickened inner 

 margin of the valve, I am of opinion that it does not attain a large size. It must not 

 be confounded with the young of Mactra achatina, also met with at the same locality. 

 That species has the hinder portion of the valves longest, and lacks the strong grooving 

 on each side of the umbones. 



Mactra decora, Deshayes. 



Madra decora, Deshayes, Proc. Zool. Soc. Lond., 1854, p. 63. 

 Mactra decora, Reeve, Conch. Icon., vol. viii. fig. 80. 



Habitat. — Banda Island. 



A single specimen from this locality may possibly be the young form of this species, 

 although I hesitate to afiirm positively that such is the case. The species attains a 

 larger size than the example figm-ed by Reeve, a specimen in the Cumingian collection 

 having a length of 57 mm. 



Mactra pusiUa, A. Adams (PL V. figs. 8-8r). 



Mactra pusilla, A. Adams, Proc. Zool. Soo. Lond., 18.55, p. 226. 



Testa ovato-trigona, fere seq^uilateralis, utrinque subacuminata, tenuis, dilute caeruleo- 

 alba, radiis olivaceo-fuscis numerosis plus minusve distinctis ornata. Umbones mediani, 

 acuti, pur[3urascentes. Ai-ea dorsalis utrinque alba, fusco margiuata. Yalvse nitidse, 

 incrementi lineis tenuibus striatije, utrinque marginem dorsalem versus subfortiter et 

 confertim sulcatiB. Margo dorsi anticus valde declivis, jjaulo convexus, posticus 

 aliquanto convexior, subsequaliter obliquus. Ventris margo regulariter late arcuatus. 

 Pagina interna livido-purpurascens, prope umbones cseruleo-albida, marginem inferiorem 

 versus dilute fuscescens vel cervina. Pallii sinus mediocriter profundus, vix ad medium 

 attingens, ad extremitatem acute rotundatum. 



