Macoma.\ PELECYPODA. 955 



Sect. 1. PSAMMOTRETA, Dall, 1900. 



Psammotreta, Dall, Trans. Wagn. Free Inst., iii, pt. 5, 1900, 1045. Type : 

 Macoma aurora, Hanley. 



Shell with the resilium internal, shorter than and partly sepa- 

 rated from the ligament. 



1. Macoma Suteri, E. A. Smith, 1898. Plate 63, tig. 13. 

 Macoma Suteri, E. A. Smith, P. Mai. S.<iii, 1898, 23, f. vi in text. 



Shell small, slightly inequilateral, very thin, whitish, finely con- 

 centrically striated. Beaks prominent, acute. Anterior end very 

 little shorter than the posterior, broadly rounded, the dorsal margin 

 lightly excavated in front of the beaks, slowly descending ; posterior 

 end much narrower, very narrowly convex, the dorsal margin straight, 

 rapidly descending ; basal margin broadly curved. Sculpture con- 

 sisting of very fine concentric striae. Epidermis very thin, grey, 

 not shining. Colour grey. Interior yellowish-white, shining, faintly 

 radially striated. Margins smooth, sharp. Hinge : Right valve with 

 2 divergent cardinals ; left valve with 1 bifid cardinal tooth. Liga- 

 ment elongate, the anterior part prominent ; there is an oblique 

 internal resilium behind the cardinals, directed backwards, con- 

 nected above with the external ligament underneath the umbones. 

 Adductor-scars unequal, the anterior large, high, and narrow, the 

 posterior large, rounded. Pallial sinus deep, rounded. 



Length, 15 mra. ; height, 12 mm. ; diameter, 5-5 mm. 



Type in the British Museum. 



Hob. Lyttelton, in 2-4 fathoms (H. S.). 



Fam. SEMELID.E, Dall. 



Animal having the mantle widely open for the passage of a large, 

 pointed, compressed, and not byssiferous foot. External gill-plate 

 directed upwards. Siphons separate and excessively long. 



Shell orbicular or elongated oval, equivalve, generally compressed, 

 with an external ligament and an internal resilum lodged in a fossette ; 

 hinge variable ; the cardinal teeth inconspicuous or obsolete ; lateral 

 teeth not constant ; pallial sinus very deep, rounded. 



Genus 1. LEPTOMYA, A. Adams, 1864. 



Leptomya, A. Adams, A.M.N.H. (3), xiii, 18(i4, 208 ; not of Conrad, 1867. 

 Type : L. cochlearis, Hinds. 



Shell small, convex, rostrate behind ; surface lamellate ; right 

 valve with 2 cardinal teeth, left valve with 1 cardinal ; there are no 

 lateral teeth ; resilifer oblique ; pallial sinus deep. 



