IHE NAUTILUS. 



VOL. XXV. DECEMBER, 1911. No. 8 



A NEW GENTJS OF BIVALVES FROM BERMUDA 



BY WILLIAM IIKAl.KY DAI.).. 



Among various minute shells scnl (or examination to the National 

 Museum by Mr. Arthur Haycock, of Bermuda, is a minute trian- 

 gular bivalve which at first looks like a very small, solid Cuminyia, 

 but on careful scrutiny under a compound microscope proves to be a 

 new genus of the family "Mesodesmaiidce. One complete specimen 

 and a single valve are in the collection of Mr. Haycock. 



AKGYUODONAX, n. g. 

 Shell small, concentrically sculptured, porcellanous, with a minute, 



smooth, nearly circular prodissoconch. Hinge formula '-^ 



R.0.1r010.0 



1'allial sinus large and deep, muscular scars large and strong; pos- 

 sessing a feeble external ligament and a narrow but strong resilium. 

 General form tellinoid. Type: 



AKGYRODONAX HAYCOCKI, n. sp. 



Shell small, white, subtriangular, attenuated behind; sculpture of 

 concentric threads growing coarser and more or less irregularly 

 grouped toward the margin ; lunular space impressed but not defined 

 by any limiting sculpture; there is no escutcheon; ligament feeble, 

 short, arnphidetic external; resilium narrow, strong, situated in front 

 of the posterior left cardinal tooth, and in the right valve in front of 

 a ridge, which may be a feeble cardinal tooth or merely the raised 



