KELLIA. 223 



metrical, and nearly triangular : lips two, of a similar shape : 

 foot long, tongue-shaped and bent, placed in the middle of the 

 front margin. 



SHELL globular : leaks incurved : cartilage cylindrical, placed 

 on the hinge-plate at the posterior side (being the broader and 

 larger end of the shell) : hinge containing in the left valve a 

 thick, erect cardinal tooth, and in each valve two remarkably 

 strong laminar teeth which are partly cardinal and partly 

 lateral. 



This genus differs from Las&a in the incurrent tube 

 being more complete and the excurrent tube conspi- 

 cuous, in the foot being placed in the middle of the 

 ventral margin (instead of on the anterior side and pro- 

 truding through a slit at the base of the larger tube), 

 but especially in the position of the cartilage, which 

 lies on the broader and larger side of the shell, sup- 

 porting the hinge-plate, and outside of the lateral teeth, 

 and not (as in the last genus) placed on the narrower 

 and smaller side of the shell, nor clasping the hinge- 

 plate inside and below those teeth. The habits of the 

 present genus are also different from those of Lascea. 

 This is not amphibious, and probably cannot exist if 

 constantly left high and dry by the receding tide. It 

 usually inhabits comparatively deep water, and prefers a 

 muddy ground. Both are viviparous : but at least one 

 species of Montacuta has the same mode of reproduc- 

 tion. In the shape of its shell Kellia resembles Sphae- 

 rium; but that genus has an external ligament and 

 differs from this in the number and arrangement of the 

 teeth. The position of the tubes is also very dissimilar 

 in these genera. In Kellia , as well as in Lasted, it is 

 somewhat anomalous, the larger and incurrent tube 

 being placed at one end, and the smaller and excurrent 

 tube at the other. In Sphcerium and most other genera 

 which have two tubes, both are placed on the same side ; 



