70 



gitudinaliter striatd indiitd ; posticd sguamis corneis, postici ro- 

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

 anticd ventrali clausd lavigatd ; valvd accessorid anticd dorsali 

 maximd, leevi, quinquelobatd ; marginibus dorsali ventraligue 

 posticis epidermide comeo-testaced obtectis : long. 2-, lat. 1-, alt. 

 1-1 poli. 

 Hab. ad Sinum Panamae. 



Obs. Testse junioris parte antica ventrali apertž, hiatu maximo ; 

 valva accessoria nulla, marginibus dorsali ventraliąue posticis haud 

 obtectis: long. 1-5, lat. 07, sdt. 07 poU. 



Tliis is another remarkable instance of extreme dissimilarity be- 

 tween the young and fuUy grown shells ; the large anterior ventral 

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

 up in the fully gro\\Ti indi^ndual ; the enonnous accessory valve co- 

 vering the umbones and spreading widely over the anterior dorsal 

 parts of the sheU 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 šame place. — G. B. S. 



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



lat. 0-25, alt. 0-25 poli. 

 Hab. ad Panamam. 

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



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

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

 areis, anticd scabriusculd ; intermedid epidermide corned lon- 

 gitudinaliter striatd indutd ; posticd sguamis corneis, postice acu- 

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

 anticd ventrali clausd, lavigatd ; valvd accessorid anticd dorsali 

 magnd, subtetragond, antice unilobatd ; marginibus ventrali dor- 

 saligue epidermide comeo-testaced obtectis, tegmine dorsali antice 

 inflato : long. 2', lat. 0'9, alt. 09 poli. 

 Hab. ad Panamam. 



Found in limestone at low u'ater. The šame sort of difFerence is 

 obser\'able 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 ąuantity 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, postice 

 obtusd, hiatu mediocri ; valvis f ascid impressd transversim sul- 



