500 



divided plates of the umbonal ridge are placed upon a broad 

 platform between them and the umbones. The postero-dorsal 

 outhne is inflated. The posterior part of the shell is covered by 

 a blackish epidermis ; at the termination, there are two horny 

 swellings, each of them bilobed, surmounting a broad, black, shelly 

 tube. 



Found in hard clay and loose stones at Monte Christo. Cuming. 



MONOGRAPH OF THE GENUS 

 TRIOMPHALIA.* 



Tam. Pholadidse. 



Char. Gen. Molluscum acephalum terebrans. Testa bivalvis, 

 setate juniori hians, setate matura clausa. Valvse insequales, 

 utraque antice lamina testacea inflata ad marginem ventralem 

 afiixa ; interne cardine unidentato, sine processu ; valva dextra 

 postice alteram valvam longitudine superans ; valva sinistra pos- 

 tice abbreviata, antice lamina ventrali alteram valvam involvente, 

 ad dorsum nucleo quasi-umbonali incipiente. 



A genus of boring Mollusca, with bivalve shells, allied to that 

 group of Pkolades which, when mature, have the ventral anterior 

 hiatus of the valves closed by an expanded test. The valves 

 are unequal, the right one being considerably produced at the 

 posterior end, and the left much shorter at that end, but anteriorly 

 extending its ventral covering so as to over-wrap that of the other. 



* Tpio, tria ; ofi<paKiov, umbo. Since writing the above, my attention lias been 

 directed to a genus of Fholadidoe, described under the name of Pholadojms (Conrad), 

 which may, by possibility, be identical with the oue now proposed. The two most 

 important characters, however, being omitted (namely, the third umbo, on which I 

 found the name ; and the absence of hinge processes, on which alone I justify the 

 separation of the genus), and no reference being made to Quoy and Gaimard's iigure 

 of Ph. fjlohosa, the description is not deemed sufficiently complete for identification. 



