160 



radiately ribbed ; ribs about 20-24, elevated, tubercularly nodose ; 

 tubercles rounded, obtuse, ventral margin strongly pectinated. 

 Hab. Cape York, 6 fathoms ; J. Jukes, Esq. (Mus. Cuming.) 



5. On a new genus of Pholadidje, with notices of several 



NEW species and OF A REMARKABLE SPECIMEN OF PhOLAS 



CALVA IN Mr. Cuming's Collection. By G. B. Sowerby, 

 JuN., F.L.S. 



(Mollusca, PI. V.) 



Among the species of Pholades there are various modifications of 

 structure, particularly with regard to the form, position and number of 

 the accessory valves, and the test enclosing the anterior hiatus of the 

 shell in some species, vv^hich are very interesting and important, and 

 have given rise to various proposals for the division of the species into 

 distinct genera. The propriety or otherwise of such divisions it is 

 scarcely worth while to argue about, as it is after all a mere question 

 of convenience, whether such modifications should be expressed by 

 arranging the species in so many genera of a family, or so many sub- 

 divisions of a genus. It will be sufficient for my present purpose to 

 remark, that there is one character in which the Pholades, whether 

 open or closed, with or without accessory valves, cup-bearing or tube- 

 forming, all agree, and that is, in the curved processes commencing 

 under the hinges inside the shell. In the genus now to be described 

 these are wanting, and this fact removes the hesitation which might 

 have been felt in attempting to establish a generic distinction from the 

 other characters, however well-marked and interesting. 



Genus Triomphalia*. 



Char. Gen. — Molluscum acephalum terebrans. Testa bivalvis, setate 

 juniore hians, setate matura clausa. Valvse insequales ; utraque an- 

 tice lamina testacea inflata ad marginem ventralem affixa, interne 

 cardine unidentato, sine processu subcardinali. Valva dextra postice 

 alteram longitudine superans. Valva sinistra alteram involvens, ad 

 dorsum nucleo quasi-umbonali incipiens. 



The shells of this genus, when mature, have the ventral hiatus closed 

 by an expanded test fixed to the edge of each valve ; that of the left 

 valve commences at the back, in a nucleus resembling an extra umbo, 

 and in front overwrapping that of the other. The right valve, on 

 the other hand, materially exceeds in length, at the posterior extre- 

 mity, the other valve, which terminates very abruptly.. The hinge is 

 without sub-umbonal processes, but has an obtuse tooth on the hinge 

 in each valve. 



The name is taken from the nucleus of the covering-test in the 

 right valve, which forms, as it were, a third umbo. The typical spe- 

 cies is the Pholas globosa of Quoy. 



Triomphalia globosa, PI. V. f. 1. (Pholas globosa, Quoy.) 

 Tr. testa subovali, postice subattenuatd, antice globosa ; valvis 

 transversa dimidiatis, parte posticd concentric^ lyratd ; in medio 



* Tpeis, tres ; dfKpaXo^, umbo. 



