MOLLUSCA. 81 



plicata, plicis undulato-corrugatis, Mc illic duplicatis, latere postico rostrato, flexuoso, acuto, antico rotun- 

 dato, umbonibus subacuminatis. 



Hab. Shores of Borneo. 



Strongly plicated obliquely, somewhat after the manner of the preceding species, but 

 wanting the radiately-ribbed posterior area. 



1. Psahjiobia rugttlosa. PI. XXIV. Pig. 4 a, 6. Psam. testa oblonga, alba, antice rotundata, obli- 

 que plicata, plicis tenuibus, confertis, undulatis, postice vix angulata, costis radiantibus squamuliferis exsculpta. 



Hab. China Sea. 



The oblique plaits are finer in this species, whilst the radiating ribs of the posterior side 

 are rather strongly developed. 



88. AMPHIDESMA, Lamarck. 



1. AiTPHiDESHA exaeata. PI. XXIV. Fig. 9. Amph. testa oblongo-ovata, alba, maculis perpaucis 

 roseis pallide adspersa, concentrice costata, costis tenuibus, acutis, subrecurvis, interstitiis profunde exca- 

 vatis, lineis pulcherrime decussatis. 



Hab. Sooloo Sea. 



Well distinguished by its numerous delicately recurved concentric ribs. 



2. Aiiphidesma simplex. PL XXIV. Pig. 11. Amph. testa ovata, crassiuscula, subtrigona, concen- 

 trice tenuissime striata, rosaceo-alba, apicibus roseis, intus aurea, latere postico breviore, subflexuoso. 



Hab. China Sea. 



This species has very much the aspect of a small Tettina. 



8. MACTRACEA. 

 89. MACTRA, Linnoeus. 



1. Mactra Thracioedes. PI. XXIII. Pig. 8. Mac. testa ovato-oblonga, inaequilatera, tenui, opaco- 

 alba, concentrice plicata, plicis rotundatis, nndulatis, corrugatis, oblique striatis, latere postico longiore, 

 subattenuato, late hiante. 



Hab. Eastern Seas. 



This very curious species is quite an abnormal form of Mactra, having much the appear- 

 ance of a Tliracia. 



90. CRASSATELLA, Lamarck. 



1. Crassatella nana. PL XXIII. Pig. 2. C. testa subtrigono-ovata, compressa, concentrice sul- 

 cosa, latere postico longiore, angulato, subflexuoso ; brunnea, rufescente obscure trifasciata. 



Hab. Eastern Seas. 



Y 



