104 MACTRID^E. 



exception of the V-shaped tooth in Lutraria, which genus in 

 our method belongs to the Myadae. 



MACTRA, Linnaeus. 

 M. STULTORUM, Linnaeus et Auct. 

 M. stultorum, Brit. Moll. i. p. 362, pi. 22. f. 4, 6; and pi. 26. f. 2. 



Animal suboval, of the palest bluish- white ; mantle open 

 throughout the ventral range, its edge is clothed with a de- 

 licate intensely white fringe of short filaments ; both siphons 

 are short, of the same length, united, covered by a fine brown 

 deposit, which appears to be independent of the epidermis 011 

 the shell ; the united tubes are never exserted more than half 

 an inch, their orifices are fringed with simple dirty pale red 

 cirrhi; the branchial, which is the longest, with 12-16, the 

 anal has 14-20. The lower part of the body is white, and 

 the dorsal range, containing the brownish-green liver and 

 ovarium, of a dull opake white. The foot is thick, long, 

 bevelled to a sharp margin, and extensible from all the phases 

 of obtuseness to the pointed lanceolate extremity. There are 

 on each side the body two suboval, brown or drab-coloured 

 branchiae, the upper the smallest, and obliquely very finely 

 striated by the vessels of the circulation. The palpi are long, 

 triangular and pointed, of an opake brown, more distinctly 

 pectinated than the branchiae, particularly on the inner sur- 

 face. It has been omitted to be stated that the anal tube is 

 provided with an exsertile hyaline valve, and our experience 

 positively entitles us to say, that the anal tube of almost 

 every bivalve is usually furnished with that appendage, the 

 use of which is doubtless to regulate the entry and issue 

 of the water, which has probably a communication with the 

 ovarium, as well as for other functional purposes, which are 

 alluded to in our remarks on the Pholadida, in the section on 

 the branchial currents. This tubular retractile valve is never 

 attached to the branchial siphon; at least we can bring no 

 instance of its presence to our recollection. 



This is a littoral animal, and often, after a gale, is abun- 



