ARCONAIA 1189 



amount of the twist. A young, or perhaps not fully adult 

 shell, shows long anterior wings, 20 millimeters in length', 

 draAvn out to a point, but these are generally more or less 

 broken away. The type is not in the Lea collection, but a 

 smaller shell presented by Cunning. 



Arconaia mutica (Heude). 



Shell solid, inflated, elongated, twisted on its axis and having 

 the hinder part bent to one side ; beaks apparently low ; anterior 

 end with a short wing above ; posterior ridge elevated, double 

 and angled in the inner valve, the two ridges widely separated ; 

 posterior end widely, obliquely truncate ; surface rather more 

 roughened than in lanccolata ; epidermis reddish-brown or 

 blackish-brown, scarcely if at all sericeous ; pseudocardinals 

 strong, triangular, ragged but not split into denticles in the 

 specimens seen ; laterals vertically striate ; muscle scars im- 

 pressed, the posterior ones long and oblique ; nacre flesh-col- 

 ored. 



Length 108, height 30, diam. 25 mm. 



China. 

 Unto contortus var. mnticus Heude, Conch. Fluv. Nank., II, 



1877, pi. XV. fig. 32. 

 Arconaia mutica Simpson, Syn., 1900, p. 860. 



Heude makes this a variety of lanccolata, but, although I 

 have seen some intermediate material, I am inclined to believe 

 it worthy of a specific rank. It is solider, more inflated and 

 rougher than lanccolata, it is not so silky, the color is more 

 reddish, the posterior ridge of what may be called the inner 

 valve is widely and angularly double, the posterior end is 

 obliquely truncate instead of being pointed as in lanccolata. 

 The pseudocardinals are more solid and triangular, and not so 

 much split. 



Group of Arconaia conjungcns. 



Shell moderately solid, slightly twisted and bent, rounded 

 in front; pseudocardinals not so much torn as in the lanccolata 

 group; not winged in front. 



