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 PHOLADID, WITH NOTICES OF SEVERAL 
NEW SPECIES AND OF A REMARKABLE SPECIMEN OF PHOLAS 
CALVA IN Mr. Cumine’s Cotuection. By G. B. Sowersy, 
Jun., F.L.S. 
(Mollusca, Pl. 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, which 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, zetate matura clausa. Valvze ineequales ; utraque an- 
ticé lamina testacea inflata ad marginem ventralem affixd, interné 
cardine unidentato, sine processu subcardinali. Valva dextra posticé 
alteram longitudine superans. Valva sinistra alteram involvens, ad 
dorsum nucleo quasi-umbonali incipiens. 
The shells of this genus, wheu 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, Pl. V. f. 1. (Pholas globosa, Quoy.) 
Tr. testd subovali, postice subattenuatd, anticé globosd ; valvis 
transverse dimidiatis, parte postica concentrice lyratd ; in medio 
* Tpets, tres; dudadds, umbo. 
