THE NAIADES OF MISSOURI 1 93 



out sculpture. Female shell broader posteriorly, marsupial expan- 

 sion formed post-ventrad, above basal line ]ust anterior to post- 

 umbonal rtdge and bounded ventrad by a furrowed rest line. Male 

 shell more trigonal in shape with post-umbonal ridge rather 

 biangulated and with a very slight radial furrow in front; dorsal 

 ridge rather prominent. 



Internal structure of both sexes about the same except a 

 higher mantle line in the female shell; cardinals double in both 

 valves; laterals single in right, double in left; branchial cavities 

 deeply basin-like; nacre blue with a tinge of yellow in the bran- 

 chial cavity, irridescent posteriorly. 



Sex Length Height Diameter Locality 



9 32 X 21 X ismrn — (Black River, Williamsville) 

 cf 26.5 X 18 X 14mm — (Black River, Williamsville) 



Miscellaneous Remarks: — Although this rare Species has 

 been found only in one locality yet a sufficient suite of shells was 

 secured to establish its novelty. One specimen was obtained 

 gravid with ova, yet it was sufficiently, although briefly, described 

 afield before it was lost as often results in a rush of field work. 

 At first the author was inclined to call this Species T. triquetra, 

 but comparisons to actual shells of typical triquetra show that it 

 is placed in the third group of Truncilla which is characterized by 

 the marsupial expansion formed by the inflation just anterior 

 to the post-umbonal ridge not extending below the basal line 

 and in which group triquetra is not classed. Lefevrei diflfers from the 

 arcaeformis of Lea in not possessing a radial depression in front 

 of the post-dorsal ridge and in not having such a prominently 

 curved post-umbonal ridge and also in not possessing such coarse 

 hinge teeth. This new and most modern Species is dedicated to Dr. 

 George Lefevre of the Department of Zoology in the University of 

 Missouri. The discovery of this new Species from the Black River, 

 Williamsville, Missouri, and also of the new Truncilla, Curtisii Frier- 

 son and Utterback, from the White River, Hollister, this State, and, 

 being the only completely described Truncillae west of the Mississ- 

 ippi, it seems fitting that these should bear the names of the two 

 associate authors and instructors who have contributed so much to 

 the science of the Naiades in their monumental work, "Studies on 

 the Reproduction and Artificial Propagation of Fresh-Water Mussels." 



(The End) 



