432 MACTRIM. 



they live together and under such circumstances retain 

 their respective peculiarities. M 'Andrew obtained both 

 at Malaga — L. elliptica on the shore, and L. oblong a by 

 the dredge, from 4 fathoms. In my cabinet is a curious 

 malformation, the specimen having an inner case or 

 double shell on the posterior side. 



The present species is the Mactra hians of Pulteney, 

 L. solenoides of Lamarck (but not of Capt. King), M. 

 hyans of Turton's ' Conchological Dictionary/ L. Sole- 

 noidea of Brown, and probably L. solida of Philippi. 

 Leach separated it from L. elliptica under the generic 

 title of Psammophila. 



Genus IV. SCROBICULA'RIA *, Schumacher. 

 PL VIII. f. 4. 



Body oval, compressed : mantle open throughout the ventral 

 range, somewhat thickened at its edges : tubes very long, sepa- 

 rate, each covered with a membranous sheath or outer case ; 

 orifices usually plain : gills of equal size : foot long and flexible. 



Shell triangularly oval or oblong, nearly equilateral, thin, 

 of a uniform white colour, gaping at the posterior end, slightly 

 and concentrically striated : epidermis slight and iridescent : 

 bealcs turned towards the posterior side, almost contiguous: 

 cartilage placed obliquely : teeth, two small cardinals in the 

 right valve, and one in the left valve, which is clasped by the 

 opposite pair ; laterals laminar, not always developed in both 

 valves, and sometimes altogether wanting. 



It is much more difficult to define this genus by a 

 correct name than by comprehensive characters. Natu- 

 ralists are perhaps over-fastidious in the former respect. 

 I should have been glad to recognize the claim of prior- 

 ity put forward by Mr. Searles Wood for Trigonella 

 (1778) if Da Costa's description would have justified my 

 doing so; but it evidently applied to Mactra rather 



* Having a little trench ; 60 called from the shape of the cartilage-pit. 



