868 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL.XX. 



YOLDIELLA CURTA, new species. 

 (Plate XCVII, fig. 8.) 



Fhascolus ovatus (?) VERRILL, Trans. Conn. Acad., VI, p. 230, 1884 ; Expl. Albatross. 

 Eeport U. S. Com. Fish and Fisheries for 1883, p. 576, 1885 (not Seguenza). 



Shell small, short-ovate, rather swollen iii the middle, with rather 

 prominent umbos, somewhat inequilateral, the posterior end the longer 

 and slightly produced. Beaks small, incurved, with a slight posterior 

 twist and a little separated from the margin. The dorsal margin is 

 nearly straight medially, both before and behind the beaks, anteriorly 

 it merges gradually into the broadly rounded anterior end, which 

 usually has an obscure, blunt angulation in the middle; ventral mar- 

 gin broadly and evenly rounded, merging gradually into the more 

 abrupt curve of the posterior end which is a little tapered, but obtusely 

 rounded without any distinct rostrum or angulatiou ; the postero-dorsal 

 margin is a little prominent, pinched up and convex, with a considera- 

 ble slope, so that the tip of the shell is but little above the middle. 

 The surface is polished and somewhat iridescent, marked only by fine, 

 irregular lines of growth. Epidermis pale greenish or brownish yellow. 

 There is a relatively very large resilium, appearing yoke-shaped or wide 

 W-shaped in the separated valves, and covering a relatively long, 

 edentulous space beneath the beaks. The teeth are compressed, 

 oblique, imperfectly V-shaped, especially posteriorly, and but slightly 

 elevated. There are six or seven in the posterior series, of which the 

 proximal ones are rather indistinct; and four distinct and two or three 

 indistinct ones in the anterior series. In a dorsal view five are visible 

 above the margin behind the beak and four before. They are not very 

 long and rather blunt, with the distal side sloping and the side next 

 the beak a little incurved and concave. 



Length, 2.6 mm.; height, 1.8 mm.; thickness, about 1 mm. 



A few live specimens, at three stations, between N. lat. 41 11' 30", 

 W. long. 66 12' 20", and K lat. 39 38', W. long. 70 22', in 499 to 1,290 

 fathoms, 1883-1886. 



This species somewhat resembles Y. frigida in form, but it is rela- 

 tively shorter, higher and less distinctly rostrated. Its hinge is also 

 quite different. The present species is peculiar in having fewer and 

 blunter teeth and a much larger resilium than most of the related 

 species. 



YOLDIELLA PACHIA, new species. 



Shell very broad, oval, considerably swollen in the middle, with the 

 length and height nearly equal; umbos rather prominent. The poste- 

 rior end is narrowed and slightly produced, but not denned by any 

 groove or carination. The dorsal margin is very obtusely angulated, 

 anteriorly it is convex and slopes pretty rapidly to the broadly and 

 evenly rounded anterior end ; posteriorly it is nearly straight at first, 

 then slopes gradually to the posterior end. The ventral margin is very 



