MUTKLA 1 35 I 



Genus MUTELA Scopoli, 1777. 



Mutela Scopoli, Intr. Nat. Hist., 1777, p. 397. 

 Iridina Lamarck, An. sans Vert., VI, 1819, p. 88. 

 Calliscapha Swainson, Tr. on Mai., 1840, p. 380. 

 Bnfira Gistel, Naturg. Hohe Schul., 1848, p. 

 Mutelina Bourguignat, Esp. Ouk., 1885, p. 11. 



Shell elongated, slightly inflated, with low, smooth beaks, 

 and a rounded posterior ridge ; surface faintly concentrically 

 grooved ; epidermis rayless ; hinge straight, having generally 

 vestiges of taxodont teeth ; dorsal scars an irregular row, ex- 

 tending downward and forward ; muscle scars irregular. 



Animal having the palpi longer than wide, not united ; man- 

 tle margin united as far as the foot, so that the branchial and 

 anal openings are closed ; outer branchiae united to the man- 

 tle to the extremity ; inner entirely united to the foot ; foot 

 tongue-shaped, somewhat produced anteriorly. Iridina cccles- 

 tis Lea, (Troschel). 



Type, Iridina exotica Lamarck. 



Although in a number of cases the shells of this group re- 

 semble those of Spatha, there are certain reasonably constant 

 conchological difl:erences. In Spatha the hinge is never den- 

 tilate, the anterior muscle scars are two in number and dis- 

 tinct, the adductor scar being placed close to the border of 

 the shell and usually vertically elongated. The dorsal scars 

 are deep and distinct, one to three in number, and the valves 

 are generally well closed all around. In Mutela the hinge is 

 either dentilate or usually shows vestiges of dentilations, the 

 anterior scars are irregular, often three in number and faint, 

 the dorsal scars are numerous and blurred, and the valves gape 

 at the anterior base and behind. The anatomical differences, 

 so far as is known are not great. In Spatha the mantle mar- 

 gin is entirely open below as in the Unionida ; in Mutela it is 

 closed below, the lobes being united as far forward as the 

 foot, as in the marine Pholadidcu. 



