THE MOLLUSCA HEDLEY. 



PHENACOLEPAS SENTA, sp. nov. 

 (Fig. 1). 



403 



Fig. 1. 



Shell cap shaped, with a protuberant and overhanging posterior 

 apex, the earlier portion thin and translucent, the older solid 

 and opaque ; adult shell asymmetrical by reason of a slight 

 spiral twist. Colour white. The nepionic shell is very smooth 

 and glossy sharply contrasting with the dull surface of the 

 remainder, depressedly turbinate, apparently two whorled but 

 swallowed past the nucleus by the older shell. Sculpture : on 

 the part next the nepionic shell there are circular growth lines, as 

 these diverge wider their interstices are crossed by longitudinal 

 lines which develop later into low small rounded ribs parted by 

 slight furrows, these are reticulated by two series of fine raised 

 threads crossing at right angles. Upon these ribs arise in quin- 

 cunx order a series of V-shaped thorns, the limbs of which are 

 directed anteriorly. A portion of the dorsal surface immediately 

 above the posterior base is selected in the accompanying figure 

 for illustrating this feature. Finally the limbs increase till they 

 meet those of their neighbours and enclose a rhomboidal space, 

 thus the marginal part of the shell becomes cancellated by a raised 

 network, oblique both to the line of growth, the axis of the shell 

 and the earlier sculpture. The minute transverse thread lines 

 persist to the aperture. 



Aperture subcircular, the edge when adult is broadened and 

 finely crenulated. Interior glossy, the exterior sculpture visible 

 through the shell. Muscular impressions are a right and left 

 adductor scar and a narrow horse shoe marking the head line a 

 little within the lip. Length 6, breadth 4|, height 3 mm. 



Eight empty shells from sand on the beach of Funafuti 

 lagoon. 



