﻿222 SIMI'SON'IA 



SiMi'SONiA DL'iCLKRCi ( Koclicbrune) . 



Shell subrhomboid. somewhat lenticular, solid, scarcely in- 

 flated, sometimes snbcompressed ; posterior rids^c low and very 

 wide, slightly bianj^ulate ; beaks not high nor full, their sculp- 

 ture not seen ; surface with irregular growth lines ; epidermis 

 apparently olive-green ; there is a low posterior wing, wliicli 

 is worn away in old shells ; hinge line nearly evenly curved ; 

 left valve probably having two pseudocardinals and two lat- 

 erals ; right valve with one strong, triangular, high pseudocar- 

 dinal, with a vestige of a small one in front of it, and one 

 remote, short, truncated lateral, which is decidedly reflexed 

 along its inner edge ; the hinge line is smooth and rounded be- 

 tween the two teeth ; beak cavities deep, with a row of pits 

 under the pseudocardinal ; muscle scars impressed, the anterior 

 roughened : nacre whitish, clouded with purplish-brown, soft 

 and shining, very thick in front ; pallial line deep. 



Length 122, height 90. diam. al^out 45 mm. 



Mekong River, Siam. 

 Undo dticlerci Rochehrune, l^ull. Soc. I'hil., VII, 1882, p. zy, 



pi. T, fig. 2 (in extract). 

 Chamherlainia dticlerci Simpson, Syn., 1900, p. 582. 

 Simpsonia dticlerci Rochebrune, Bull. Mus. Hist. Nat., 1904, 



p. 465. 



Two right valves much worn and eroded were donated to 

 the National Museum by Mr. John B. Henderson, Jr. The 

 short lateral is reflexed as it is in LcfJdodesma and the nacre, 

 which is peculiarly clouded, is very greatly thickened in front. 



SiMi'SONiA DEMANGEi Rochebrune. 



"Shell verv thick, compressed, elongate-ovate, inequilateral, 

 gaping in front, with a slight posterior wing; laminately, con- 

 centrically sulcate, deeply eroded, dark blackish-brown, irreg- 

 ularly radiately costate, w^ith broad, flat, interrupted folds; 

 dorsal margin almost straight, slightly oblique, anterior mar- 

 gin small, rounded and somewhat produced : posterior margin 

 subtriangular. subcomi)rcssed ; basal margin the longest, al- 

 most straight, slightly undulated; beaks small, compressed. 



