502 



Tliis species is larger than T. globosa (f. 54, 55), the ventral 

 covering being much more globose and rough ; the supplementary 

 nucleus is not so flat or so smooth ; the points at the termination 

 of the right valve are more strongly curved ; the concentric ribs 

 on the posterior part of the valves are more strongly defined, and 

 they are not crossed by the oblique row of raised points which 

 characterize those of the other species. Nothing can exceed the 

 beauty of sculpture in both species. 



West Colombia ; soft stone, low water. Cuming. 



3. Triomphalia Cumingii (pi. cvi. f. 56, 57), Sowerby,junr., 

 Pro. Zool. Soc, 1849. 



T. testa rotunda, crassa ; valvis postice canali divisis, concentrice 

 lineis elevatis lyratis, antice costis minutis, serratis, radiatis ; parte 

 postica concentrice laminata ; valva dextra postice in lingula tri- 

 angulari margine triplicato producta ; valva sinistra postice brevis- 

 sima, margine terminali circidari. 



This shell would be completely spherical, but for the linguiform 

 triplicate extension of the right valve ; the left valve terminating 

 in a circular margin, where the round part of the right meets it. 

 The posterior part of the valves is very narrow, and strongly 

 laminated ; the anterior part is striated, and, near the termination, 

 transversely ribbed. The covering test of the hiatus is beautifully 

 rounded. 



Coral rock, at low water ; Isle of Zebu, Philippines. Cuming. 



MONOGRAPH OF THE GENUS 

 XYLOPHAGA. 



Char. Gen. Molluscmn acephalum terebrans. Testa bivalvis, 

 antice angulatim hians, globosa, cardine edentulo, umbonibus 

 valvis duabus parvis obtectis. 



This genus, like Triomplialia, wants the subumbonal processes 

 wliich are characteristic of Pholas and Teredo. 



