dall: mollusca and brachiopoda. 379 



different in the specimens collected; and also on account of the presence of the 

 impressed lines on the disk. These differences would ordinarily be regarded as 

 specific, and unless the range of variation in Leda calcar is much larger than usual, 

 •will prove to be specific in the present case. 



TOLDIINAE. 



YOL.DIA MoLLER. 

 Yoldia MoUer, Ind. Moll. Groenl., 1842, p. 18; Ist species, yoWf'a hyperborea Lov^n. 



Moller's first species, which lie erroneously identified with the arctica of Gray, 

 is of the same group as the better known Y. limatula Say. His second and only 

 other species, which he described under the name of Y. angularis, is synonymous 

 with Y. thraciaeformis Storer. 



The first species is generally recognized as the type of the genus. It has the 

 ligament external, reduced to a mere film or obsolete nonfunctional remnant, 

 sometimes focusscd in a minute spot just behind the beaks, sometimes amphi- 

 detically spread along the hinge margin but distinguishable, if at all, only by its 

 darker brown or blackish color from the periostracum with which it is continuous. 

 In some of the southern species, however, there is a well-defined functional opistho- 

 detic ligament, and for these it seems reasonable that the character should be rec- 

 ognized by a sectional name. For this the name Katadesmia is now proposed 

 with the following species as type. 



Yoldia (Katadesmia) vincula Dall, n. sp. 



Plate 5, figure R. 



Shell having on a small scale much the form of Sanguinolaria rosea, equivalve 

 inequilateral, white with a pale olivaceous periostracum, smooth, brilliantly pol- 

 ished ; beaks low, very inconspicuous, nearer the anterior end ; lunule and 

 escutcheon narrow, sublanceolate, elongate, defined by small elevated ridges ; ex- 

 ternal ligament about one fourth as long as the escutcheon, opisthodetic; anterior 

 end evenly rounded from beaks to base ; posterior end attenuated and pointed, 

 the posterior basal margin obliquely truncated, extreme point gently rounded and 

 laterally compressed; interior opaque white, showing little trace of muscular im- 

 pressions, the margins entire; chondrophore and resilium, internal, triangular, 

 vertical, not very large; anterior hinge margin with fifteen, posterior with about 

 twenty-five teeth. Lon. of shell, 14 ; of beaks behind the anterior end, G ; alt. 8 ; 

 diam. 4.5 mm. 



U. S. S. "Albatross," station 3360, in 1672 fathoms, sand. Gulf of Panama, 

 bottom temperature 42° F. U. S. N. Mus. 122.008. Also at stations 3354 and 

 3361, in 322 fathoms, mud, bottom temperature 46° F., and 1471 fathoms, green 

 ooze, temperature 36°. 6 F., respectively. 



The species is notable for its pale color and brilliant polish. 



