RECTIDE^NS 1 1 63 



Rectidens GRACius (Strubell). 



"Shell much elongated, siibcompressed, rather thin, delicate- 

 ly, costulate striate, not at all shining-, brownish-olivaceous, 

 very inequilateral, squarely truncate in front, much elongated 

 posteriorly. Dorsal margin forming an angle with the very 

 short anterior margin ; posteriorly it runs into the posterior 

 slope with a rounded angle; ventral margin horizontal, not at 

 all ascending posteriorly, forming with the posterior margin 

 a depressed, subvertically truncated rostrum. Umbones an- 

 terior, deeply eroded ; areola subobsolete ; area elongate, com- 

 pressed, with two obsolete carinae extending from the beaks; 

 ligament thin, quite long. Hinge thin; with two, elongate, 

 oblique, compressed, low teeth in the right valve, almost reach- 

 ing the margin ; cardinal tooth elongate, with obsolete lamellae ; 

 muscular impressions indistinct. Nacre bluish-white, iridescent 

 posteriorly. 



Length 55, height 23, diam. 12.5 mm." (Strubell.) 



Type locality. South Sumatra. 

 Microndylcra gracilis Strubrll, Nachr. Deutsch. Mai. Ges., 



1897, p. 8. 

 Rectidens gracilis Haas, Conch. Cab., Unio, 1912, pi. 27, fig. 6. 



"It dififers from M. hageni not only by its much more striate 

 surface, but also by its heavy, stronger development of the 

 hinge-teeth." (Strubell). 



Haas, (1. c), figures U. palemhangeiisis Strubell and 

 U. paJiumhacnsis von M^artens as synonyms of this species. 



Rectidens palkmbangensis (Strubell). 



"Shell very long ovate, very inequilateral, delicately and 

 closely striate, here and there roughly costate-sulcate, posterior 

 end distinctly biangulate, scarcely shining, rather thin, oliva- 

 ceous, overlaid with a thin gray deposit. Anterior end very 

 short, posterior elongate. Dorsal margin very slightly obhque, 

 forming with the very short, rounded, subtruncate anterior 

 margin a distinct angle and with the sloping posterior margin 

 an indistinct one ; ventral margin almost straight, slightly 

 ascending posteriorly to the roundly-acuminate, depressed 



