MACTRA. 105 



dantly cast on the Warren Sands, at Exmouth, from whence 

 we obtained our finest specimens. 



M. SUBTRUNCATA, Da Costa. 



M. subtruncata, Brit. Moll. i. p. 358, pi. 21. f. 8; and pi. 22. f. 2; 

 (siphons) pi. L. f. 3. 



As the external organs of the Mactrce 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 branchiae and palpi are of 

 a pale brown, and that the foot is of a paler yellow, narrower 

 than in its congener the M. stultorum. We have in 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. SOLIDA, Linnaeus. 



M. solida, Brit. Moll. i. p. 351, pi. 22. f. 1, 5; (siphons) pi. L. 2. 

 M. truncata, Brit. Moll. i. p. 354, pi. 23. f. 1 ; and iv. p. 253. 



The animal, like the M. stultorum, has the margin of the 

 mantle fringed; 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, w T hich 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 branchiae 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 ; in some it is flat-sided, tumid, and 



