REPORT ON THE LAMELLIBRANCHIATA. 89 



with the hinder slope. The interior of the valves is somewhat glossy towards the outer 

 margins, whilst in the centre and subumhonal region it is minutely suljgranular. It is 

 also marked with a faint radiating substriation. The anterior nmscular scar is very 

 elongate, pyriform, and not nearly so broad as the posterior. The siphonal inflection is 

 broad, and terminates in a sharply rounded extremity far beyond the middle of the valves. 

 From this extremity a shallow groove extends towards the beaks, and a similar impressed 

 ray (although insignificant) is generally ol:)servable radiating from llic uuilio to the inner 

 margin of the posterior adductor scar. 



Length 18 mm., height 12, diameter Sf. A smaller specimen is 12| long, 8^ high, 

 and 3^ in diameter. 



Habitat. — Station 85, near the Canaiy Islands; depth, 1125 fathoms. Station 73, 

 west of the Azores; depth, 1000 fatlioms. Station 98, west of Sierra Leone, in 1750 

 fathoms. Station 244, Mid North Pacific, at a depth of 2900 fathoms. 



Two specimens from the last locality I fail to distinguish from those from the 

 Atlantic. They may be a little narrower and not Cjuite so acute posteriorly, but with the 

 exception of these trifling and possibly individual peculiarities I can discover no essential 

 specific differences. Ahra longicallus (Scacchi) closely resembles this species, but is a 

 little narrower, not quite so acute at the posterior end, and has a shallower pallial sinus. 



Semele (Theora) iridescens (Hinds) (PI. V. figs. 6-6h). 



Necera iridescens, Hinds, Proc. Zool. Soc. Lond., 1843, p. 78. 

 Theora iridescens, H. and A. Adams, Gen. Eec. Moll., vol. ii. p. 370. 

 Theora iridescens, A. Adams, Ann. and Mag. Nat. Hist., 186-4, vol. xiii. p. 209. 

 Theora iridescens, Tryon, Amer. Journ. Concli., vol. iv., Appendix, p. 118. 



Testa tenuis, subhyalina, vitreo-alba, valde nitida, inasquilateralis, 8ec[uivalvis, 

 utrinque anguste hians, antice lata, rotundata, postice cuneata, paulo veutricosa, 

 incrementi lineis striata. Margo dorsi anticus primo vix arcuatus, dein oblique curvatus, 

 posticus recte declivis. Ventris margo late arcuatus, postice leviter sinuatus. Umbones 

 mediocriter magni, supra cardinem paulo prominentes. Denies cardinales duo ante 

 fossam ligamenti in valva dextra coUocati, unicus in valva sinistra. Denies laterales 

 utrinque tenues, prominentes. Fossa cartilaginis obliqua, intus recedens. Sinus paUii 

 magnus, profundissimus. Pagina interna radiatim et confertim striata. 



Length 17^ mm., height 11, diameter 8. 



Habitat. — Amboina, in 15 to 20 fathoms (Challenger) ; Island of Luzon, Philippines 

 (Hinds) ; Yobuka, Japan (A. Adams). 



The above description is drawn up from the t}-pe specimens in the British Museum, as 

 the single valve obtained by the Challenger is but immature. From this it will be seen 

 that the details of the hinge do not correspond with the description given by Messrs. 



(zool. CHALL. EXP. — PART XXXV. — 1885.) Mm 12 



