230 LUCINIM. 



According to Valenciennes, the animal of Lucina has but 

 a single gill-leaflet on each side. Forbes and Hanley 

 state that there can be little doubt that two lamellse 

 on the same side are so united as to appear like a single 

 gill. Deshayes has shown that the two gills when 

 divided contain four rows of vessels, and that they 

 occupy as much space as all the gills in other Con- 

 chiferous mollusks. As I do not pretend to be, like 

 Sidrophel, " old dog at physiology," I can say no more 

 than that I hope the question may be sooner or later 

 set at rest. The foot is a remarkable and peculiar 

 organ. When at rest and contracted, it looks like a 

 shrivelled worm, and is doubled up within the shell ; but 

 when the period for action has arrived, the wrinkles 

 disappear, and in a marvellously short time the foot 

 expands and is drawn out to three times the length of 

 the whole body. It is thus rendered firm and more 

 capable of muscular exertion. This distention is effected 

 by means of aquiferous ducts or canals, which permeate 

 the tissue of the foot, the water being introduced at its 

 base through a wide funnel opening directly into the 

 visceral cavity. A similar organization of the foot has 

 been noticed in the Cephalophorous mollusks, especially 

 in some of the Muricidce, Naticida, and Bullidae, which 

 have the same habit of burrowing as the Lucinidce. 

 Another peculiarity which characterizes the present 

 family is the elongation of the anterior adductor muscle ; 

 and it is easy to recognize the fossil species by the nature 

 of the scar or mark inside the shell. The ligament is 

 more or less external in all the genera but Loripes, 

 which has an internal cartilage concealed within the 

 hinge-line and occupying an oblique groove, as in Kellia. 

 The Lucinida inhabit sandy mud and gravel, in which 

 they shelter themselves. Very many recent species of 



