TRIBE ARCACEA. 167 
ligament is short and a very small part is posterior to the 
umbones.} 
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 
hollow ; beaks contiguous, posteriorly inflected; ligament mar- 
ginal and partly internal, inserted in the cardinal hollow. 
* Lanceolate. 
N. Lanczoxata. Lam. 1.—Sow. G. f. 1.—Conch. II. 
Nucula. f. 1.—Reeve. t. 84. f. 1. Extremely long, thin, fragile, 
hyaline, anterior side lanceolate and rather obtuse, the posterior 
equally long but obtuse and broader, ventral margin entire.— 
NXipixapt. 
N. Eroneata. Sow. Z. P. 1832.—Con. Il. 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.  %,..2,7,.—West 
Colombia. 
N. Tevurnorwes. 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 les of growth decussated by very fine oblique 
striee, dorsal edges convex. +..2.—Cumana. 
N. Paraconica. D’Orbigny. Lanceolate, very narrow, de- 
pressed, rather fragile, equilateral, rounded posteriorly, extremely 
attenuated anteriorly, with very fine concentric striz ; 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. 4..13.—Patagonia. 
N. Crentrera. Sow. Z. P. 1832.—Reeve. t. 84. f. 3.— 
Con. Il. f. 3. Transversely elongated, lanceolate, smooth, with 

1 The P. Assrmizis 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 Flammzeus though certainly distinct 
is only described from worn specimens. So too is the P. Longior 
of Sowerby. 
