3. 



liVlien tlie animal is taken, from the mud. in ^Afiaich it lives, 

 the anterior portion of the shell is jet black. Posteriorly it 

 gradually assiunes olive greeai. The black is no doubt a stain, 

 as it bleaches out in animals kept in aquaria, and the shell as- 

 sumes a rather laniforra olivaceous tint, somewhat streal^ed along 

 some of the more prominent, lines of gro"VTth with yellow or brown. 



On each valve, two more or less prono\xncod radial stripes 

 extend from the beal-c to the ventral margin, one anterior, the 

 other posterior, figure 1. The margin of the mantle opposite 

 the extremity of each of these stripes is specially modified 

 and sen.sitive. Internally, near the dorsal margin of each valve 

 are two rows of toxodont teeth, one extending anteriorly a:ad the 

 other posteriorly from the cartilage pit, figure 2. Near tlie car- 

 tilage pit these teeth are very small and closely placed. They 

 attain their greatest length about midway along each row, and be- 

 come short and rather widely separated at the ends furth^est from 

 the cartilage pit. 



Internal markings are rather obscure. Beside the foot 

 and adductor muscle scars, and the pallial line with its deep and 

 broad sinus, there is on each valve" a rather distinct, cur^red 

 line, extending from the ventral margin of the anterior adductor 

 muscle scar, nearly to the cartilage pit. Dissection shows that 

 this line marks the limit of the genital mass and digestive glaid. 



