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. 
YOLDIINAE. 
XOILDIA MÖLLER. 
Yoldia Möller, Ind. Moll. Groenl., 1842, p. 18; 1st species, Yoldia hyperborea Lovén. 
. Möller’s first species, which he erroneously identified with the arctica of Gray, 
is of the same group as the better known F. 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 nonfunetional remnant, 
Sometimes focussed in a minute spot just behind the beaks, sometimes amphi- 
detically spread along the hinge margin but distinguishablo, if at all, only by its 
darker brown or blackish color from the periostraeum 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 Darr, n. sp. 
Plate 5, figure 5. 
. Shell having on a small scale much the form of Sanguinolaria rosea, equivalve 
Mequilateral, 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, 6 ; alt. 8; 
diam. 4.5 mm. 
U.8. 8, « Albatross,” station 8360, in 1672 fathoms, sand, Gulf of Panama, 
bottom temperature 42° F. U.S. N. Mus. 192,903. Also at stations 3354 and 
3361, in 399 fathoms, mud, bottom temperature 46° F., and 1471 fathoms, green 
Ooze, temperature 369.6 F., respectively. 
+ The species is notable for its pale color and brilliant polish. 
