IIOO AKCONAIA 



Group of Arconaia lanceolata. 

 Shell with an anterior wing. 



Arconaia LANCEOLATA (Lea). 



vShell elongated, solid, subinfiated, twisted on its axis, 

 curved to the right or left from the middle to the extreme 

 posterior end, with a strong anterior wing, which is carried 

 forward to a point ; posterior ridge well developed, subangular 

 or narrowly rounded, fullest on the convex side of the shell, 

 ending in a blunt point below an oblique posterior truncation ; 

 beaks but little elevated ; surface with irreg'ular growth lines, 

 often with a few nodules or subvertical corrugations at the 

 anterior of the disk ; epidermis ashy brown, somewhat silky ; 

 pseudocardinals strong, double in each valve, usually much 

 split up ; laterals very long, more or less vertically striate, two 

 in the left valve and one in the right ; muscle scars well im- 

 pressed, the posterior ones long and oblique ; dorsal scars 

 numerous; nacre whitish. 



Length 130, height 34, diam. 22 mm. 



China. 

 Triquetra lanccolafo Lea, Pr. Ac. N. Sci. Phila., VIH, 1856, 



p. 79. 

 Hyria lanceolata IvEa, Pr. Ac. N. Sci. Phila., 1856, p. 300. 

 Arconaia lanceolata Conrad, Am. Jl. Conch., I, 1856, p. 234. — 



Simpson, Syn., 1900, p. 860. 

 Triquetra contorta Lea, Pr. Ac. N. Sci. Phila., YIU, 1856, 



p. 300; Obs., VL 1857, p. 39, pi. XXXIII, fig. 33; Jl. Ac. N. 



Sci. Phila., Ill, 1858. p. 319, pi. xxxiii, fig. 33. 

 Hyria contorta SowERl'.^', Conch. Icon., XVTI, 1869, pi. i. figs. 



2a, 2b. 

 Margaron (Triquetra) contorta Lea, Syn., 1870, p. 26. 

 Unio contortus Heude, Conch. Fluv. Nank., II, 1877, pi. xv.. 



fig- 31- 



Several examples of this remarkable shell are before me, 

 most of which turn to the right behind ; one, however, curves 

 strongly to the left. One of the shells curves but little and 

 there is quite a little variation in this matter, as well as in the 



