152 ARCAD.E. 



of transverse indentations may be seen along eacli side of the pos- 

 terior hinge-margin. 



[The above comparisons were made with specimens sent from 

 England, none of which are now regarded as the true N. nucleus; 

 and since two or three species have been eliminated {N. radiata, de- 

 cussata., nitida, &c.) the remauider seem in no respect to differ from 

 the American shell. 



Nucula expansa. 



Shell large, ovate-triangular, tumid, dusky, cliestuut-colored surface, distinctly 

 waved, and with line radiating strias on both dorsal areas. 



Nucula BeUotii, Adams, Zool. Proc. (1836), ]). 51. — IIanlev, in Sowb. Thcs. Conch. 



iii. 102, pi. 229, fig. 128. — Packakd, Labr. Mar. Sh. 13. 

 Nucula expansa, Reeve, in Belcher's last Arct. Voy. 397, pi. 33, fig. 2 (1855). 



Sliell large, thin, ovate triangular, tumid, without marked umbonal 

 ridges ; anterior dorsal margin nearly vertical and straight, the area 

 broad heart-shaped, depressed, bounded by an obtuse ridge and 

 marked by fine diverging striae, anterior end rounding 

 ^'^1«^ into the decidedly arcuate ventral margin ; posterior dor- 

 sal margin much longer and more oblique than the an- 

 terior, gently curved, and with no angles ; dorsal face 

 broad, somewhat flattened, with the lips of the valves 

 scarcely pouting, and with a few delicate radiating lines ; 

 surface concentrically ridged, quite coarsely so at the 

 N. ^x^nsa outcr circlcs ; epidermis glossy, dark chestnut, with yel- 

 lowish zones. Interior leaden color, muscular impres- 

 sions deep, margin simple, covered by the inflected epidermis ; hinge 

 rather robust, the ligament spoon very oblique, with about ten teeth 

 in front and fifteen behind it. Lenti'th, eleven twentieths of an 

 inch ; height, seven twentieths of an inch ; breadth, six twentieths 

 of an inch. 



Dredged by Dr. Packard in fifteen fathoms at Chataquc Bay, 

 Labrador ; Arctic Seas (^Hanlcif) ; Beechey Island (^Belcher). 



One of the largest and finest of the genus, so remarkable for its 

 undulated surface and dark epidermis as to assimilate it to Corbicula. 



Nucula inflata. 



Shell trapeziform, oliliquely truncated, tumid, beaks prominent, anterior. 



Nucula inflata, Hancock, Ann. Nat. Hist. (1846), 333, pi. 5, figs. 13, 14. — Hanley, in 



SowB. Thes. Conch, iii. 162 {Nucula), pi. 4, figs. 115, 116. 

 Nucula tennis, Moller, Moll. Gncnl. 17. 

 Nucula ohiiquala, Beck (1847), teste Mokcii. 



