70 



gitudinaliter striatd indntd ; posticd squamis corneis, postice ro- 

 tundatis, imhricatis, lavibus, gradatim minoribus, ornatd; parte 

 anticd ventrali clausd Icevigatd ; valvd accessorid anticd dorsali 

 maximd, leevi, quinquelobatd ; marginibus dorsali ventralique 

 posticis epidermide corneo-testaced obtectis : long. 2', lat. !•, alt. 

 1- 1 poll. 

 Hab. ad Sinum Panamse. 



Obs. Testae junioris parte antica ventrali apert^, hiatu maximo ; 

 valva accessoria nulla, marginibus dorsali ventralique posticis baud 

 obtectis: long. 1"5, lat. 0*7, alt. 0'7 poll. 



This is another remarkable instance of extreme dissimilarity be- 

 tween the young and fully grovi^n shells ; the large anterior ventral 

 opening, so conspicuous in the young shell, being completely closed 

 up in the fully grown individual ; the enormous accessory valve co- 

 vering the umbones and spreading widely over the anterior dorsal 

 parts of the shell is also a remarkable addition formed at its full 

 growth. 



Found in Spondyli, at a depth of twelve fathoms, at the Isle of 

 Perico in the Bay of Panama : the young shells have also been taken 

 out of hard stones at low water in the same place. — G. B. S. 



Pholas calva, var. nana. Phol. calva, testd nand : long. 0'5, 



lat. 0-25, alt. Q- 25 poll. 

 Hab. ad Panamam. 

 Found in hard stones at low water. — G. B. S. 



Pholas acuminata. Phol. testd ovatd, antice rotundatd, postich 

 acuminatd, hiatu minimo ; valvis singulis in areas tres divisis ; 

 areis, anticd scabriusculd ; intermedid epidermide corned lon- 

 gitudinaliter striatd indutd ; posticd squamis corneis, postici acu- 

 minatis, imbricatis, Icevibus, gradatim minoribus, ornatd ; parte 

 anticd. ventrali clausd, lavigatd ; valvd accessorid anticd dorsali 

 magnd, subtetragond, antice unilobatd ; marginibus ventrali dor- 

 salique epidermide corneo-testaced obtectis, tegmine dorsali antice 

 inflato : long. 2", lat. 0"9, alt. 0'9 poll, 

 Hab. ad Panamam. 



Found in limestone at low water. The same sort of difference is 

 observable between the young and fully grown shells in this species 

 as in Phol. calva. 



One specimen of this shell in Mr. Cuming's collection merits 

 particular notice. It demonstrates a fact of considerable importance 

 to geologists. It is in argillaceous limestone, very much resem- 

 bling lias, and in forming the cavity in which it resides, it has, by 

 such chemical process as frequently takes place, absorbed a much 

 greater quantity of the rock than could be retained or converted ; 

 this is again deposited at the upper part of the cavity; and thus the 

 rock is recomposed. — G. B. S. 



Pholas melanura. Phol. testd ovatd, antice rotundatd, postici 

 obtusd, hiatu mediocri ; valvis fascid impressd transversim sul- 



