TRIBE ARCACEA. 167 



ligament is short and a very small 'part is posterior to the 

 wnhones.^ 



NUCULA. 



Transverse, oval-trigonal, or oblong, equivalve, and equilateral; 

 no ligamental area ; teeth of the hinge linear, numerous, and 

 pectinated, interrupted in the middle by an oblique produced 

 hollom ; beaks contiguous, posteriorly injlected ; ligament mai'- 

 ginal and partly internal, inserted in the cardinal hollow. 



* Lanceolate. 



N. Lanceolata. Lam. 1. — Sow. G. f. 1. — Conch. II. 

 Nucxda. f. 1. — Reeve, t. 84. /. 1. Extremely long, thin, fragile, 

 hyaline, anterior side lanceolate and rather obtuse, the posterior 

 equally long but obtuse and broader, ventral margin entire. — 

 Xipixapi. 



N. Elongata. 6'ow. Z. p. 1832.— Con. II. f. 2.~-Reeve. 

 t. 84. f. 2. Transversely elongated, lanceolate, thin white with a 

 fuscous epidermis towards the ventral margin : subequilateral but 

 rather shorter posteriorly ; dorsal margin rather straight, anteriorly 

 subreflected : anterior row of teeth divaricate. t^-.2/j. — West 

 Colombia. 



N. Tellinoides. Sow. G. f. 2.— Arca T. W. S. t. 2. 

 f. 3. Lanceolate, transversely elongated, subequilateral, anteriorly 

 subangulated, posteriorly rounded, sides nearly equal in depth; 

 white, thin, the lines of growth decussated by very fine oblique 

 striae, dorsal edges convex. ^ . . 2. — Cumana. 



N. Patagonica. D' OrUgny. Lanceolate, very narrow, de- 

 pressed, rather fragile, equilateral, rounded posteriorly, extremely 

 attenuated anteriorly, with very fine concentric striae ; ventral edge 

 entire, little arcuated in the centre, and sloping, obliquely at each 

 end; dorsal edges little sloping the anterior one incurved and 

 excavated above; teeth very numerous, cardinal pit broadly tri- 

 angular. J . . 1 ^. — Patagonia. 



N. Crenifera. Sow. Z. P. \S32.— Reeve, t. 84. /. 3.— 

 Con. 11, f, 3. Transversely elongated, lanceolate, smooth, with 



1 The P. AssiMiLis of Sow. in Z. P. 1832. is most closely 

 allied (if indeed distinct from) this species. 



See too Spurcus, Cancellatus and Pertusus of Reeve in the 

 Zoological Proceedings, which should be compared with the young 

 of the other species. His Flammseus though certainly distinct 

 is only described from worn specimens. So too is the P. Longior 

 of Sowerby. 



