104 MACTRID As. 
exception of the V-shaped tooth in Lutraria, which genus m 
our method belongs to the Myade. 
MACTRA, Linnezus. 
M. stuttorum, Linneus et Auct. 
M. stultorum, Brit. Moll. i. p. 362, pl. 22. f. 4, 6; and pl. 26. f. 2. 
Animal suboval, of the palest bluish-white; mantle open 
throughout the ventral range, its edge is clothed with a de- 
hieate intensely white frmge 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 on 
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 
branchiz, 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 branchiz, particularly on the imner 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 Pholadide, in the section on 
the branchial currents. This tubular retractile valve is never 
attached to the branchial siphon; at least we can bring no 
istance of its presence to our recollection. 
This is a littoral animal, and often, after a gale, is abun- 
