YOLDIA. 



157 



growth, over whicli 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. 8iphonal 

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

 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 {Morch). Mr. Hanley has 

 indicated a suljgenus 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 with a dark olive-green epidermis; 

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

 both ends. 



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

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

 Recent Shells, Biv. 169, pi. 20, fig. 1.5. — Sowerby, Thes. Couch, pi. 1, figs. 4, 13. 



Leda thracicpformis, Stuipson, Shells of New England, 9 (1S.")1) ; Inv. Gr. Manan, 20. 



Xuciila na'iculans, Couthouy, Journ. Bost. Soc. ii. 178, pi. 4, fig. 4 (young). — Gould, 

 Inv. Mass. 103. 



Yoldia /hraciceformis, Morch, Moll. Groenl. 21 (1857). — Moller, Prod. Moll. Grand. 21. 



Yoldid nncjularis, Moller, Moll. Groenl. 17, and in Mus. Amsterdam. 



Nuculnlalermiria, Valexc. Vny. of Venus, Moll. jil. 23, fi^. 5. 



Yoldia MWleri, Gray, Voy. of Fly, Append, ii. 3G1, 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 

 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, 

 lengthened notch between the centre of the base and the wave ; the 



1'. thraciajorinis. 



