YOLDIA. 157 



growth, over which the epidermis rises like a very delicate fringe. 

 Hinge with the ligament spoon broad, deep, very slightly oblique, 

 and with twelve to fourteen stout teeth on each side of it. i?i})lional 

 sinus quite obvious. Length, eight tenths of an inch ; height, five 

 tenths of an inch ; breadth, three tenths of an inch. 



Found in a semi-fossil condition in the clays about Portland and 

 Montreal. It is found in a recent condition in the Arctic seas ; 

 Beechey Island (^Belcher}', Greenland {March). Mr. Hanley has 

 indicated a subgenus Portlandia, to receive this and a few other 

 species which are conspicuously emarginated below the tips, and 

 closed at both ends. 



Yoldia thraciseformis. 



Fig. 66. 



Shell kidney-shaped, inequipartite, covered Avith a dark olive-green epidermis; 

 a rib-like wave passes from the beaks to the posterior-inferior angle ; gaping at 

 both ends. 



Nucula thracio'formis, Storer, Best. Joiirn. Nat. Hist. ii. 122 (woodcut). — Gould, Inv. 

 Mass. 97, fig. 66. — De Kav, Nat. Hist. New York, 178, pi. 12, fig. 217. — Hanley, 

 Recent Shells, Biv. 169, pi. 20, fig. 1.5. — Sowerby, Thes. Conch, pi. 1, figs. 4, 1-3. 



Leda thracio'formis, Stimpson, Shells of New England, 9 (IS.'il) ; Inv. Gr. Manan, 20. 



Nucula naricularis, Couthouy, Journ. Bost. Soc. ii. 178, pi. 4, fig. 4 (young). — Gould, 

 Inv. Mass. 103. 



Yoldia thracia^formis, MoRCH, Moll. Gra?nl. 21 (1857). — Moller, Prod. Moll. Groenl. 21. 



Yoldia angularis, Moller, Moll. Grronl. 17, and in Mus. Amsterdam. 



Nucula lalernaria, Valexc. Vny. of Venus, INIoll. j)!. 23, fis. 5. 



Yoldia Miilleri, Gray, Voy. of Fly, Append, ii. 361, pi. 2, fig 4. 



Shell oblong-ovate, or rather kidney-shaped, somewhat pointed 

 before, broadest and truncated 



behind, thin ; gaping at both ^' 



ends ; inequilateral ; the beaks 

 considerably elevated, pointed, 

 inclined backwards, and touch- 

 ing each other, are situated 

 near the anterior third of the 

 shell ; an obtuse, rib-like wave 

 passes obliquely over the shell 



from the beaks to the posterior y thradaformis. 



third of the basal margin, divid- 

 ing the surface of the shell into two unequal triangles ; the outline 

 of the anterior triangle is regularly curved, excepting a shallow, 

 leno'thened notch between the centre of the base and the wave ; the 



"■s" 



