MACTRA. 105 
dantly cast on the Warren Sands, at Exmouth, from whence 
we obtained our finest specimens. 
M. susprruncata, Da Costa. 
M. subtruncata, Brit. Moll. i. p. 358, pl. 21. f.. 8; and pl. 22. f. 2; 
(siphons) pl. L. f. 3. 
As the external organs of the Mactre are very similar, it 
will only be necessary to mention the variations of some of 
the succeeding species from the M. stultorum, which may be 
considered the type of the genus. The present animal differs 
in having no fringe to the margin of the mantle, at least none 
could be detected ; the siphons are united as in M. stultorum, 
and clothed with an evanescent epidermis; the orifices have 
simple pale red, white or yellow cirrhi; and we may conclude 
our account by observing, that the branchize and palpi are of 
a pale brown, and that the foot ts of a paler yellow, narrower 
than in its congener the M. stultorum. We have im this 
instance, and one or two others, departed from the usual plan 
of a detailed description ; it is an example of the inconvenience 
attendant on the omission, as we are here obliged to have 
recourse to our notes of another species to complete the 
present one. We think, if possible, such references should 
be avoided. 
M. soxipa, Linnzeus. 
M. solida, Brit. Moll. 1. p. 351, pl. 22. f. 1, 5; (siphons) pl. L. f. 2. 
M. truncata, Brit. Moll. i. p. 354, pl. 23. f. 1; and iv. p. 253. 
The animal, like the M. stultorum, has the margin of the 
mantle frmged; the siphonal canals, as to structure and 
arrangement, are the same as in the two former species, and 
of a pale brown colour; the branchial one, which is the 
largest, has about sixteen, and the anal twenty, shorter pale 
yellow, or brown, or reddish cirrhi at their orifices, which vary 
greatly in different localities. The branchiz and palpi differ 
from the preceding animals in being of a deeper brown, with 
a decided reddish hue ; otherwise they are of the same shape, 
and nearly with similar pectinations. The M. solida varies 
in shape in every locality ; im some it is flat-sided, tumid, and 
