LIOPISTHA LIBAXOTICA. 39 



Liopistha Libanotica, sp. nov. 



Plate VI, tigs. 7 a, b, c. 



JVitckiis ovaio-ohJonc/us, cequivalvis, valde inceqidlateralis ; aniice brevior, sub- 

 ventricosus, ahnipte decUvis ac subrofundatus ; depressio lunularis mcifjim, profunda, 

 margimbus valvarum exsiantibus medio divisa ; postice productm, elevcdus, compressus, 

 siib/ntncaftts, pauhtin hians : mnbones anfemediani, prominentes, lafi, tiimidi, incurvi, 

 maxime approximati : superficies concentrice tenuitcr sidcata : ligamentum externum : 

 cardo, linea pcdlii et impressiones muscidares ignotce. 



Cast ovately oblong, equivalve, very inequilateral ; before (shorter than 

 behind, rather ventricose, abruptly inclined and subrotundate ; lunular de- 

 pression large, deep, divided in the middle by the projecting margins of the 

 valves ; behind produced, elevated, compressed, subtruncate, slightly gaping : 

 umbones anterior to the middle of the valves, prominent, broad, swollen, 

 incurved, closely approximate : surface concentrically and lightly sulcate : 

 ligament external : hinge, pallial line, and muscular impressions unknown. 



Three specimens, internal casts. 



Largest : lengtli, 102 inm. ; height, 80 mm. ; thickness, 56 mm. 



One figured : " 76 mm.; " 61mm.; " 42 mm. 



Smallest: " 73 mm.; " 52 ram. ; " 36 mm. 



As seen from the side, the form and proportions of the specimens strik- 

 ingly resemble Liopistha frequem Zittel, from the Cretaceous of Gosau (first 

 described by Zittel as Panopcca frequens *), and Poromyu superba Stoliczka, 

 which, with the other species assigned by that author to the same genus, are 

 conclusively proved by Meek t to belong, not to Poromya of Forbes, but to 

 his own Liopistha, — a classification which has been adopted by Zittel. t In 

 tlie dorsal view, tlie casts are seen to be mucli less ventricose than superba, 

 and somewhat less so than frequens ; while the three species agree in the char- 

 acter of the lunular and dorsal areas, as do the present species and frequens in 

 their compressed posterior extremities. Traces of teeth are absent from the 

 casts. A short and rather wide oval cavity or pit, just beliind the beaks, 

 seems adapted to the gaping and ".short and erect fulcra" (Meek, op. cit., 



* Deukscliriftcii dor Kais. Akad., Math. Natui'wisscnscli., XXIV, p. Ill, PI. i, figs. 5 a-g, Wien, 1865. 

 t Invert. Cret. aud Tert. Foss. of Upper Missouri Countrv, p. 229, Wasliiugton, 1S76. 

 X Handbuch der Palaeontologie, I. Baud, 2. Abtlieilung, p. 131, Muiicheu, 1881. 



