428 mactridjE. 



separated : teeth as in Mactra, except that the laterals in the 

 present genus are very small or rudimentary : pallial scar 

 having a deep sinus. 



In comparing this genus with the last, we find that 

 the siphonal tubes in Lutraria are extremely long ; that 

 the shell is large, oblong, very inequilateral, and gapes 

 widely at each end ; and that the lateral teeth are much 

 less developed than in Mactra, and in one species alto- 

 gether wanting. The Lutraria burrow deeply in mud 

 near the shore. 



Clark proposed to merge the present genus in My a ; 

 and there has been much controversy as to its syste- 

 matic position. It has certainly strong affinities both 

 with Mactra and My a. The last, however, has its man- 

 tle more closed, the tubes completely united, and a dif- 

 ferent kind of hinge-process. 



1. Lutraria ellip'tica *, Lamarck. 



L. elliptica, Lara. An. sans Vert. v. p. 468 ; F. &H. i. p. 370, pi. xii., and 

 (animal) pi. H. f. 2. 



Body white : mantle open only for one-third of its extent, 

 margined by rather distant fine white filaments : tubes taper- 

 ing ; sheath between two and three times as long as the shell 

 is broad, white towards its base, variegated in the middle with 

 zigzag purplish-brown blotches, which at the top become dis- 

 tinct dots of a deeper hue ; the surface of the sheath is also 

 marked with two or three circular brown lines, an inch apart, 

 and it is covered with a transparent corrugated skin, w T kich 

 appears to be an extension of the epidermis that clothes the 

 shell ; orifices of the tubes encircled by numerous white cirri 

 minutely spotted with dark purplish -brown or red ; the cirri of 

 the alimentary tube are longer than the other set, and minutely 

 ciliated at their sides : gills pale brown, not deep, the upper 

 pair rather smaller than the lower ; they are hung transversely, 

 and finely pectinated : palps of a paler colour, long, triangular, 

 pointed, of fine texture, and delicately striated: foot large, 



thick, and extensile. 



* Elliptical. 



