870 PROCEEDINGS OF TSE NATIONAL MUSEUM. VOL.XX. 



The pallial sinus is rather wide and moderately deep, but is invisible 

 in most specimens. 



Length of the largest specimen. 3.G mm.; height, 2.3 mm. 



A number of specimens, at about fifteen stations, between !N". lat. 

 42 33', W. long. 09 58.5', and K lat. 35 12' 10", W. long. 74 57' 15", 

 in 100 to 705 fathoms, 1878-18SG. 



This species is distinguished from Yoldiella frigida, and most of the 

 other small species which it resembles, by its narrower, or lower, and 

 more compressed form, more delicate shell, straighter dorsal margin, 

 and the more central prolongation of the posterior end. It is appar- 

 ently more nearly related to the smaller species, I", minuscula, than 

 to any other. The latter has a smaller, shorter, and more swollen 

 shell, more convex veutrally, with the hinge-margin somewhat more 

 angulated. 



YOLDIELLA MINUSCULA, new species. 

 (Plato LXXIX, figs. 2,7.) 



Toldia Jeffreys! VERRILL, Trans. Conn. Acad., VI, pp. 229, 279, 1884; Expl. 

 Albatross, Report U. S. Corn. Fish and Fisheries for 1883, p. 576, 1885. 



Shell minute, broad-ovate, covered with microscopic, pretty regular 

 concentric striations, with a very lustrous, somewhat iridescent, yel- 

 lowish epidermis. The two ends are nearly equal in length; the 

 posterior somewhat narrowed and obtuse at the end, the anterior well- 

 rounded. The uinbos are not prominent and the beaks are very small 

 and project but slightly above the margin. The antero-dorsal margin is 

 slightly convex at first, and nearly horizontal, and passes gradually 

 into the curve of the anterior end; ventral margin is broad and nearly 

 uniformly convex ; the posterior end is a little produced in the middle 

 and forms there a slight obtuse angle; the postero-dorsal margin is a 

 little convex and nearly horizontal at first and then slopes rather 

 rapidly to the tip. The hinge-margin is thin and delicate; the two 

 series of teeth lie nearly in a straight line but the anterior one is a 

 little oblique, so that they form a very wide angle at the beaks where 

 the resilium entirely interrupts the hinge-margin forming a wide notch 

 without any definite pit or shelf; the teeth are small, very oblique, and 

 only slightly prominent; there are only about five in the anterior and 

 six in the posterior series. 



Length, about 2.3 mm.; height, about 1.5 mm. 



Only a few specimens, at four stations, between N. lat 41 53', W. 

 long. 65 35', and N. lat. 38 27', W. long. 73 2', in 705 to 1,200 

 fathoms, 1883-1885. 



This very minute species may, with a larger series, prove Jx) be the 

 young of some of the preceding species. 



