216 PKOCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



line into an arched wing-like prominence above the ligament, "which 

 latter is just visible between its lips. 



In colour the shell is variable, being sometimes entirely white, 

 sometimes tinged with pale yellow, or pale violet or red on the older 

 part of the shell. The internal surface is either white, violet, or 

 reddish-brown, the hinge-plate strong, bearing on the right valve 

 a roundish rugose anterior lateral, and the middle cardinal is also 

 thick and rugose ; the teeth of the left valve are normal. Pallial 

 sinus deep, ascending, sometimes rounded, and sometimes bluntly 

 angular at the anterior end. The I'ight valve has ^a short but deep 

 groove on the posterior margin. 



This species is distinguished from all others by the fine longitudinal 

 radiating riblets which covei' its surface and are irr9,r,ularly nodulated 

 by very fine concentric incised lines or striae. In size, shape, 

 concentric sculpture, and dentition D. lucinalis much resembles 

 D. htstrio, but the escutcheon area is very different. The elevation 

 of this area into a wing-like projection is not a character of more 

 than specific importance. Other species show it in a less degree, 

 .such as I), piibescens, D. Japonica, and D. prostrata, and the degree 

 of elevation varies even in the same species. 



"With respect to habitat, this also can now be established. The 

 locality given by Lamarck is the island of St. Thomas, but this was 

 probably a mistake. The locality of Sowerby's type of D. driatissima 

 was unknown, but that of amethystina is given as Australia, and 

 Mr. Smith inforuis me that the British Museum also possesses 

 a specimen of striatissima (i.e. the white variety) from the Monte 

 Bello Islands (West Australia), collected and presented by Mr. T. H. 

 Haynes, so there can be no doubt what part of the world is the real 

 home of this interesting species. 



