Occasional Papers of the Mnseiun of Zoology 13 



Elliptic (Sphenonaias) liebmanni (Philippi) (1847), 



subspecies cuatotolapamensis, new subspecies 

 Plate I, figs. 6, 7; plate III, fig. 22 (type) ; plate IV, figs. 20-25. 



Twenty specimens ; including odd valves ; from Rio San 

 Juan (H, vii, c). 



Shell of medium size, elongate subelliptical to subrhomboid, 

 quite solid, convex, with posterior ridge well marked, sub- 

 angular or often rounded and sometimes double ; beaks well 

 anterior, sculpture (as interpreted from remains of smallest 

 specimen) probably somewhat similar to that oi B. plexus, 

 only not so oblique, and broken by the radial plications so as 

 to give it an almost radial appearance (at least suggestive of 

 some of the South American genera) ; anterior end evenly 

 rounded or subangular just in front of lunule ; posterior mar- 

 gin gradually curved, sometimes quite markedly biangulate 

 behind ; basal line very slightly rounded to subsinuate, post- 

 basal point but little elevated; epidermis (in older shells) dark 

 brown to almost black, roughened to smooth and shiny, with 

 fine, radiating striations (in younger shells with golden-yellow 

 ground-color, almost completely obscured by diffuse olive-green 

 rays) ; surface of shell usually marked by vertical furrows 

 (which start high on the beaks and more or less disturb the 

 beak sculpture), most prominent on and just behind the ante- 

 rior slope, usually not extending more than 30 mm. ventrad 

 from the beaks, and rarely by radiating, dorsally curved plica- 

 tions as in B. plexus; left valve with two pseudocardinals, the 

 anterior compressed, almost lamellar and very oblique, the 

 posterior trigonal or compressed ventrally so as to be wedge- 

 shaped, and two, elongate, almost straight laterals, of which 

 the more ventral is better developed; right valve (II, 22) usu- 

 ally with two, subequal, compressed, almost lamellar, and very 

 oblique pseudocardinals, although sometimes the anterior is 



