154 



truncated at its extremity ; base semi-ovate. Beaks small, approximate, 

 depressed, curved inwards and a little forwai'ds, anterior, but not quite 

 terminal. Behind the beaks the superior margin ascends, first in a broad 

 and very slightly convex curve, after which it slopes gradually and gently 

 downwards to the upper margin of the posterior end. Lunule not very 

 distinctly defined, shortly and broadly lanceolate in outline, rather 

 deeply excavated. In the rear of the beaks there are two areas, one of 

 which is inside the other. The inner area, which appears to extend 

 from the beaks to the posterior termination of the hinge line, is narrowly 

 lanceolate, as seen from above, deeply excavated, and bounded on both 

 sides by a sharp keel. The outer area is indicated only by an oblique 

 flattening of the valves above, in the direction of a line which might be 

 drawn from the beaks to the lower extremity of the posterior end, and 

 its outline is broadly lanceolate. The hinge teeth are unknown, but the 

 ligament was certainly external. 



Surface marked by numerous concentric striae, and, on the central and 

 lower portion of the shell only, by four concentric grooves or arrests of 

 growth, of which the first and second are well defined and wide apart, 

 and the third »nd fourth more obscure and closer together. 



Sucia Islands, in Division A ; J. Eichardson, 1874. A single specimen, 

 with the test partly preserved on both valves, but imperfect at the anal 

 end. In the figure the outline of th3 posterior termination of the shell 

 has been restored from the lines of growth, and to some extent also from 

 the shape and markings of the cast. 



L^VICARDIUM SUCIENSE. (N. Sp.) 

 Plate 18, figure 3. 



Shell convex, inequilateral, obliquely and ovately subtri angular, 

 narrowest above and widest near the base ; length and height nearly 

 equal. Anterior side short and rather broadly rounded ; posterior side 

 somewhat longer, obliquely truncated at its extremity, and bluntly 

 pointed at its junction with the ventral border ; base broadly semi-ovate, 

 rounded in front and flatter behind. Beaks large, prominent, approxi- 

 mate, incurved, directed also a little forwards, and placed in advance of 

 the middle; umbones gibbous. No well defined lunule; posterior area 

 narrow, flattened obliquely, and margined near the beaks by an obtuse, 

 subangular keel or ridge, which becomes obsolete long before I'eaching 

 the base behind. 



Surface polished, shining, marked only by minute and crowded, but 



