^^ 



Ihe Nautilus. 



Vol. XXV. DECEMBER, 1911. No. 8 



A NEW GENUS OF BIVALVES FROM BERMUDA 



BY \V 11,1,1AM IIK\LEy DAM.. 



Among various minute shells sent lor examination to tiie National 

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

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

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

 new genus of the family Mesodesmatidce. One complete specimen 

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



Akgyrodonax, n. g. 



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



. ,1 A- 1 w r 1 L.l.OrlOl.l. 



smootli, nearly circular prodissoconch. Hinge formula 



^ "^ R.O.lrOlO.O 



Pallial sinus large and deejt, muscuhir scars large and strong; pos- 

 sessing a feeble external ligament an<l a narrow but strong resilium. 

 General form tellinoid. Type : 



Argyrodonax haycocki, n. sp. 



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

 concentric threads growing coarser and more or less irregularly 

 grouped toward the margin ; liinular space impressed but not defined 

 by any limiting sculpture; there is no e.scutcheon; ligament feeble, 

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

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

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



