501 



On the dorsal edge, at the umbones, this testaceous covering 

 seems to take its rise from an extra-umbonal nucleus. Hinge 

 unidentate, without processes. The over-wrapping of the ventral 

 covering of the right valve by that of the left, the umbo-like 

 nucleus of the latter, and the compensating inequality of the 

 valves at the posterior end, would be considered by many concho- 

 logists as forming sufficient grounds for separating this peculiarly 

 constructed group from the genus Pholas. But were the separa- 

 tion to rest upon these characters alone, it might be said that, in 

 consistency, the generic division of other groups of PJ/olades, pro- 

 posed by authors, some of which present very interesting peculi- 

 arities, should also be adopted. But the groups named as genera, 

 Dactylus, Pholadidcea, Talona, and Jouanettia, all exhibit one 

 character in common, namely, the curved processes jutting from 

 beneath the hinge, which in Triomphalia are wanting. The name 

 is taken from the nucleus of the anterior lamina, which, over- 

 lying the two umbones, forms, as it were, a third. 



1. Triomphalia globosa (pi. cvi. f. 54, 55). Pholas glo- 

 bosa, Quoy, Voy. Astrolabe. 



T. testa subovali, postice subattenuata, antice globosa ; valvis 

 transverse dimidiatis : parte postica concentrice lyrata, in medio 

 costa imbricata una ; parte antica lyrata, radiatim costis acute im- 

 bricatis ornata; valva dextra product;!, sublinguiformi, dentibus 

 acutis recurvis serrata; nucleo lamina? terminalis valva? sinistra 

 triangulari, striato, subcomplanato. 



Bather oval, thin, with the valves transversely divided, with one 

 radiating series of angidar points in the middle of the posterior 

 half, and eight or nine on the anterior portion, crossed by raised 

 lines beautifully curved in the opposite direction. The right valve 

 terminates angularly, and is serrated at the edges by curved, sharp 

 teeth. 



In soft stone at half-tide ; Isle of Leyte, Philippines. Cuming. 



2. Triomphalia pulcherrima (pi. cvi. f. 58, 59), Sowerhy, 

 junr., Pro. Zool. Soc, 1849. 



T. testa, subovali, ventricosa, postice globosa, corrugata, antice 

 subattenuata ; valvis transverse dimidiatis : parte postica costis 

 distantibus concentrice lyrata ; parte antica lineis lyrata, costis im- 

 bricatis radiata ; valva dextra producta, linguiforrni, margine den- 

 tibus acutis crispatis serrato; nucleo lamina? terminalis valva? sinistra?, 

 subtriangulari, rotundo, lineis elevatis lyrato. 



3 T 



