136 



duce a scar ; therefore it would appear difficult to fix Mactra 

 otherwise than to follow the Cardiada, and come into line 

 between them and the Cyprmida. 



SYNDOSMYA, Recluz. 



S. ALBA, Wood. 



S. alba, Brit. Moll. i. p. 316, pi. 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 branchiae 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 

 branchiae are carried round the mouth without a solution of 

 continuity, as in the Arcada ; 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 intensely white spots. The liver is 

 green, and the ovarium of a bluish-white colour, fall of ova in 

 August. 



This is an aberrant genus of the Tellinidce ; 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 Tellinidae and Anatinidae. At one time we 



