2OO BY THE DEEP SEA. 



is usually coloured some shade of brown, with a number of 

 white bands radiating from the beak. The hinge arrange- 

 ments in this genus are worthy of note, as indeed they 

 are in all the genera, and must be carefully studied by anybody 

 who wishes to have anything more than the merest superficial 

 knowledge of conchology. 



In the Trough-shells the ligament of the hinge is short and 

 thick, and contained in a spoon-like cavity in each valve. 

 Immediately in front of it there are two shelly teeth, joined 

 above in the form of a A, and from each side of the beak there 

 runs off a strong ridge-like tooth, the surface of which is 

 " milled" like the edge of a shilling or a sovereign. The 

 Elliptic Trough-shell (M. elliptica) is not so triangular as M. 

 stiiltorum, and is without the white rays. The Cut Trough- 

 shell (M. truncatd) might be appropriately styled the hatchet 

 shell, for its truncated ends give it a very close likeness to the 

 head of a hatchet. 



, Related to the Trough -shells are the Otter-shells (Lutrarid), 

 of which we have two species. They burrow in the mud and 

 sands, of estuaries especially, and are found from low-water 

 to about twelve fathoms. Having found a complete, though 

 empty-shell, you will be surprised to discover that it will not 

 close properly, and you not unnaturally suppose that you have 

 got hold of a malformed specimen, whose shell has got a twist 

 somehow. That, however, would be a mistake, as you would 

 find when other specimens came in your way, and you found 

 they all had the same objection to closing at the ends. From 

 one end, when the creature is alive, protrude its united 

 syphons, large and thick ; and from the other end is thrust 

 out the useful "foot," with which its burrowing is effected. 

 Where you happen to find the usually broken valves of the 

 Otter-shells, it is worth while to dig in the muddiest spots 

 thereabout at extreme low-water, and you will probably be 

 rewarded with perfect specimens, and have the greater satis- 

 faction of seeing the living creature within. 



