REPORT ON Tin: LAMELLIBRANCHIATA. 261 



gnuiulatis, undiqvie instrurta, .stni.s(|uo iiicreiueiiti ;L'([ualiter coiifeiti.s sculpta, 

 epidermide fi))rosa margiuem versus iiiduta. Area dorsalis angusta, hand profunda. 

 Ligamentum laiicculatuin, jileruiiKjue hand ante umlioiies productum. Pagina interaa 

 albida, fusco tincta, vel [nupureo-Fusca. Umbones pauIo promiuentes, iucurvati, cin-iter 

 in ^—^ longitudinis colloeati. 



Like many species of this genus, tliis is rather irregular in form, some specimens 

 being longer in proportion than others, and rather different in outline. They are for 

 the most part fairly convex, very inequilateral, rounded at tlie anterior end, and 

 oblicjuely, but curvedly, truncate behind. The ventral margin is somewhat parallel with 

 the hinge-line, at times exhibiting a slight median sinuation. The valves are not 

 very solid, sculptured with very numerous radiating and concentric strise, with very 

 slender granular ridges or lira^ between them, and clothed towards the outer margin 

 with a brown fibrous epidermis. The colour is variable, some specimens being wliitish 

 and faintly tinted with pale brown, whilst others are more uniformly brown. The 

 umbones are moderately prominent, about one and a half millimetres apart, and some 

 distance in advance of the centre. The ligamental area is narrow, and imly a little 

 sunken, the ligament usually extending from the posterior end to a little Ijehind the 

 beaks, where it is truncated. The interior varies in colour from whitish, more or less 

 stained with brown, to a uniform purple-brown. The hinge-teeth are small and 

 numerous. 



Length 31 mm., height IS, iliameter 16. 



Habitat. — Station 162, otf East Moncoeur Island, Bass Strait, in 38 fathoms (Chal- 

 lenger); Hudson's Bay, Port Pliilip, Sdutli Australia, attached to sea-weed, in 4 J 

 fathoms (Brit. Mus.). 



The Challenger specimens and those in the British .Museum from the latter 

 locality are precisely similar in every respect, but differ slightly in one or two points 

 from those in the Cumingian collection, also said to liave come from Port Philip. 

 These are much darker coloured within, Avhich probably in this instance is not a very 

 important distinction, as they appear to be slightly diseased, and the ligament extends 

 somewhat in front of the umbones, whilst in the Challenger shells and the others fi-om 

 Port Philip it is suddenly truncated a little behind them. This, I think, is probably 

 due to age, for the two types in Cuming's collection appear to l)e older shells than 

 the others under examination, and the largest of tlie latter shows a slight tendency to 

 prolong the ligament more forward than it is in 3'ounger specimens. 



Notwithstanding these difterences, I believe that they all l)elong to one and the 

 same species. Area jmrm, Sowerby, from Ducie's Island, is an aUieil form, differing in 

 being a little narrower, more finely sculptured, and in having the umbones rather 

 more remote from the centre. 



