48 



concava, ad latera paululum elevata; valva dextra ad umbonem 

 valde convexa, ad marginera valvam alteram superante ; 

 auriculis latis, rectangulatis, striatis, concavis ; costis 14, 

 in valva sinistra sub-quadratis, angustis, in valva dextra 

 latioribus, rotundatis, interstitiis planis ; colore fusco-nigres- 

 cente vel rubescente, intiis fulvo-nebuloso. Long. 3. 50. ; lat. 

 1. j alt. 3. 20.; poll. 



Rounded, ventricose, smooth, with the left valve concave at 

 the apex, rather elevated at the sides, the right valve very 

 convex at the apex, overlapping the other valve at the 

 margin ; the auricles are wide, rectangular, striated, concave ; 

 the ribs are 14 in number, in the upper valve they are narrow 

 and nearly square, in the lower they are wider and rounded, 

 with smooth interstices. The colour is blackish or reddish 

 brown ; the inside clouded with ligh t brown. 



9. P. Sinensis, (pi. xvi. f. 120? 121, 134.) nobis. 



T. rotundata, ventricosa, concentrice striata ; auriculis 

 concavis, striatis, valva sinistra valde concava, costis centra- 

 libus duodecim, quadratis, complanatis, sulcatis, angustatis ; 

 lateralibus parvis ; interstitiis latis, concentrice striatis ; valva 

 dextra ventricosa ; costis latis 14, rotundatis, obsolete radiatim 

 sulcatis, interstitiis angustis, margine alteram valvam 

 superante ; colore fulvo-rufescente, fusco-maculato, et 

 angulatim lineato. Long 3. 10.; lat. 0. 70.; alt. 2. JO. ; 

 poll. 



Differing from P. fuscus in having the upper valve deeply 

 concave, the ribs flatter, the interstices concentrically striated. 

 The prevailing colour is light reddish brown, mottled with 

 darker brown ; near the umbones outside the greater part of the 

 inside and two or three ribs white. China. 



10. P. Ziczac. (pi. xvi. f. 129 to 133.) Linn. Syst. Nat. 

 p. 1144. 



T. rotundata, ventricosa, la3vi ; auriculis magnis, rectangu- 

 latis, distanter sulcatis ; valva sinistra complanata, lateribus 

 planis; costis 31, depressis, alternatis, interstitiis angustis, 

 minutissime striatis ; valva dextra costis viginti quatuor, latis, 

 prope umbonem obsoletis, interstitiis nullis ; colore variegato. 

 Long. 3. 60; lat. 0. 90.; alt. 3. 30.; poll. 



Rounded, ventricose, smooth ; the auricles having one or two 

 broad slightly raised ribs on the upper part ; the upper valve 

 flat, with a broad area on each side destitute of ribs, the ribs 

 31 in number, the intermediate ones filling up the inter- 

 stices so that only narrow serrated grooves remain ; the 

 lower valve radiated with 23 grooves, which are nearly obsolete 

 near the umbones. The variations in colour are numerous, 



