from the varie'' ^ ~ ving" tho ti^bs o:" ^ ' ii?al 



'-:- i'jCii -:g . '. . ' . "^e higher and the i ' c wider. 



In th.e case of the variety under discussion 'is 



-11;^ more "ororrAnent on left valves than : ' ' . 



is especially pronoimced on in:niat^ire valves. At ' ' ti;iie 



th.e exaggeration of the earinal rih tends to cause ' rina to 



he ""on^^r th?.n "'.n the typical h a it ens e . thus caix?: ' t 



^oroiL^iG uiOii QL ;he engle iDetween the ventral and pos" " ^ 

 a fecture v/hich again is more rierhefl on immatiire valves. 



The yon.:-- of Z_, [ ?rr'-",ujn l f^at'^nenge Lall (l), a species from 

 the Gatun hec's oi Jr'anasia, also characterised hy a p:. 



(l). Trans. "Jagner Free Inst. Sci., Philadelphia, vol. , 'z , 

 5, p. 1100-1101, 1900. 



inal rih, " " " ■" r from the iovvden foi-m "by having a more oblique 

 poster'. i^gin, a narrower posterior area, v/ider, lower and 



niore rouiy^'^ri ^^if^^-'' ' ^i-, tprior 7:'vhn^ separ.?""' ' "\, 'h nar'^o'.' 



i-r interspaces and a prominent smooth area i -ly "before i 



behind t'le umbo. Tlie Ohipolan G, alicula -Dall (2) of the sarie 



[?.), I'Vm, p. 1103, pi. 4^;, fig. 5. 



; Lse a,re narrower -^.-vco^i ^ ■ '■>, fy.A. -.Mrir • ■:■-,■.-■ i-.n r■.^ ^.r'\_r\o- 



