THE NAUTILUS. 



VOL. XI. FEBRUARY, 1898. No. 10. 



UNIO (LAMPSILIS) AMPHICHJENUS, N. Sp. 



BY LORRAINE S. FRIER8ON. 



Shell large, oblong oval, thin, slightly inflated, gaping for one- 

 Lalf its length at the anterior and basal part, and at the upper part 

 of the posterior end, and covered with a shining, black or brownish 

 epidermis which is decidedly wrinkled in places ; growth lines 

 strong and irregular ; beaks but slightly prominent ; hinge line 

 evenly curved ; hinge teeth but feebly developed, there being a 

 single, compressed, rather sharp cardinal in the left valve of the 

 young shell which becomes blurred and shows a tendency to split 

 up in the older shells, and two rather short, faint laterals, the inner 

 of which is the stronger ; these being placed at the extreme poste- 

 rior end of the hinge plate, with one cardinal, and sometimes a 

 faint one above it, and a single, compressed, short lateral in the 

 right valve ; laterals ending abruptly at the posterior end, with the 

 inner edges slightly curved upwards ; area between the teeth nar- 

 row and rounded ; muscle scars distinct, and quite deep for so thin 

 a shell ; posterior retractor scar completely united with the adduc- 

 tor, dorsal scars to the number of five or six extending in a row from 

 the cavity of the beaks just behind their greatest projection towards 

 the anterior base; pallial line showing a tendency to break up into 

 several lines, and distinct traces of a posterior sinus ; nacre clouded, 

 varying from deep violet to bluish and white. 



Length 106, height 63, diam. 36 ram. 



Habitat, Sabine River at Logansport, Louisiana. 



