136 TELLINIDA. 
duce a scar ;—therefore it would appear difficult to fix Mactra 
otherwise than to follow the Cardiade, and come into line 
between them and the Cyprinide. 
SYNDOSMYA, Recluz. 
S. atBa, Wood. 
S. alba, Brit. Moll. i. p. 316, pl. 17. f. 12, 13, 14. 
Mactra Boysii, Montagu. 
Animal suboval, compressed, very pale bluish-white ; mantle 
open, with the margin dentated. The branchial and anal 
siphons are separate from the bases, very elastic both laterally 
and longitudinally ; when in full action cylindrical, and 
ordinarily as long as the shell, often much longer, The 
animal can inflate them to three times their usual diameter ; 
they are light brown, the effect of an epidermis, the ground 
colour being white; when half exserted they are strongly 
corrugated. The branchial siphon is truncate and simple at 
the orifice; the anal has the usual tubular hyaline valve, and 
is otherwise plain. The branchie are a pair on each side, 
suboval, pale brown, symmetrical, hanging obliquely from the 
dorsal range; in our small specimens we could not satisfy 
ourselves on the character of the palpi, but think the large 
branchiz are carried round the mouth without a solution of 
continuity, as in the Arcade; they are well pectinated within 
and smooth without. The foot is large in proportion to the 
animal, muscular, slightly angulated at the heel, lanceolate, 
white, without a byssal groove. The ventral portion of the 
body is marked with imtensely white spots. The liver is 
green, and the ovarium of a bluish-white colour, full of ova in 
August. 
This is an aberrant genus of the Tellinide ; in the shell and 
organs of the animal it presents singular departures from what 
we have been accustomed to consider the typical points of 
their organic structure. This genus requires a careful exami- 
nation of its species, which may eventually, in conjunction 
with Scrobicularia, lead to the formation of a family inter- 
mediate to the Tellinide and Anatinide. At one time we 
