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



The identification of this species either from the description given by Lamarck or 

 that in Reeve's work would be quite impossible ; but, having the specimen delineated in 

 the Conchologia Iconica for comparison, I am able to state that the few valves from the 

 above localities probably belong to it. They are, however, paler in colour, lack the 

 brown stain on the anterior side within the valves, and the denticles within the outer 

 margin are rather more grooved. Reeve's sliell is said to have come from the west 

 coast at Swan River. 



Pectunculus heddomei, n. sp. (PL XVIII. figs. 1—1/;). 



Testa subcompressa, rotundata, crassa, antice peculiariter radiatim constricta, alba 

 vel dilute fuscescens, hie illic fusco maculata, radiatim costata, costis circa 24 parum 

 elevatis, rotundatis, quam sulcis intermedianis valde latioriljus, incrementi lineis confer- 

 tissimis elevatis, undulatis insculpta. Pagina interna alba, utrinque supra cicatrices 

 fusco radiata, sa^pe marginem versus fusco tincta. Margo internus plerumque alba, 

 dentibus circiter 17 latis concavis munitus. 



This species is about as long as high, rather fiat, roundish, and solid. It is of a 

 white or light brown colour, spotted and stained with dark rich lirown upon the radiat- 

 ing ribs. These are very broad, flattened, rounded at the top, and much wider than 

 the grooves separating them, indeed, they almost, join one another at their leases. They 

 are about twenty -four in number, those on each side being consideraljly more slender 

 than those down the middle. The remaining sculpture consists of closely packed wavy 

 conspicuous sublamellated lines of growth which pass over and between the costse. At 

 the anterior end there is a faint depression which radiates down the valves, marking oft', 

 as it were, a large prominent lunule. The ligamental area is deep and narrow, slightly 

 separating the acute beaks. The hinge-plate is moderately broad, white, and furnished 

 with seven to ten oblique denticles, forming a slightly curved series on each side. The 

 interior is white at the middle and towards the umbones, but generally more or less 

 stained with lirown, nearer but not upon the margin. The muscular scars always have 

 a broad dark lu'own ray upon them, and are bordered within by a raised edge. The 

 margin of the valves is white, shallowly scalloped at the edge, and armed within with 

 about seventeen broad flattened concave denticles. 



Length 42 mm., height 44, diameter 22. 



Length 42 mm., height 41, diameter 21. 



Habitat. — Station 162, oft' East Moncoeur Island, Bass Strait, in 38 fathoms; sand 

 and shells. 



This species is remarkable on account of its Ijroad and not much raised ribs, and 

 the dark brown rays on the muscular impressions. The depression down the anteiior 

 side is not very conspicuous, but apparently })resent in all specimens. 



