1906. J MOLLUSKS FROM THE PERSIAN GULF. 807 



OSTREA IMBRICATA Lam. 



P.G. & M.C. Very general, often found growing in colonies 

 on the telegraph- cable, between 30 and 55 fathoms, mud. 



OsTREA iRiDESCENs Gray. 



P.G. On telegraph-cable, attaining a very large size. 



OsTREA (Alectryoxia) townsendi Melv. 



P.G. At the entrance of the Gulf, the finest examples adhering 

 to the telegraph-cable. Since this species was described (Mem. 

 Manch. Soc. vol. xlii. (1898) No. 4, p. 27, pi. ii. fig. 14), Mr. 

 Townsend has forwaixled many examples, mostly adhei'ing in 

 threes and fours together, from near Shaikh Shuaib Island and 

 elsewhere. It is probably generally distributed, though somewhat 

 local, and is undoubtedly, as already mentioned in our intro- 

 ductory remarks, probably the most beautiful and symmetrical 

 species of Oyster known, both as regards shell-texture and delicate 

 coloration. 



Fam. PECTINIDiE. 



Amussium caducum E. a. Smith. 



I. &, P.G. Karachi. Also dredged in the Gulf of Oman, 

 667-811 fathoms, by s.s. ' Investigator' {E. A. Smith). 



Originally described from the Philippines (Rep. 'Challenger' 

 Exped., xiii. Lamellibr. p. 309, j)l. xxiii. figs. 1-1 c). 



Amussium formosum Melvill, sp. n. (Plate LY. fig. 7.) 

 A. testa parva, tenuissiinia, albida, suhpellucida, inceqttivalvi ; 

 vcdvcc sinistra majore., fere Icevi, costulis radiantihus evanidis, 

 auricidis inceqitalibus, pidchre in utraque valva cancellatis ; 

 valva dextra sub lente concentrice delicatissime lirata : pagina 

 interna costis ad 10-12 instructa, liaud ad marginem valvce 

 sinistrce j)rodAictis, 

 Alt. 9, lat. 8-50, dia7n. {valvce sinistrce maj.) 1 mm. 

 Hob. Persian Gulf: Gulf of Oman. Lat. 24° 58' N., long. 

 56" 54' E. ; 156 fathoms. 



Allied to A. siebenrockii Sturany, .but much smoother, with 

 I'udimentary radiating ribs only ; there is also no sign of cancel- 

 lation on the left valve ; the right valve is much the smaller, and 

 is microscopically concentrically lirate. The internal white ribs, 

 ten to twelve in number, are not produced to the ventral margin, 

 as is the case in A. siebenrochii. 



Many examples, but mostly in imperfect condition. 



Amussium siebenrockii Sturany. 



Amiossiimi siebenrockii Sturany, Exped. S.M. Schiff ' Pola ' in 

 das Rothe Meer (1899), p. 15, Taf. iv. figs. 5-8. 



P.G. Gulf of Oman. Lat. 24° 58' N., long. 56° 54' E. ; 156 

 fathoms, shell-sand. Some specimens prettily marked with opaque 

 white and fawn-colour. 



Proc. Zool. Soc— 1906, No. LIT, 54 



