NO. lO NEW BRACK lOPODS COOPER 3 



cline), forming an angle of about 90° with the lateral commissure. 

 Shell costate ; costae broad and rounded with narrower interspaces. 

 The ribs are salmon-colored, and the interspaces are yellow. 



Ventral valve subpyramidal, gently convex in lateral profile. Fold 

 low, defined by two central costae which are a little broader and 

 more elevated than their fellows. In the sulcus between these two 

 costae a rib is intercalated near the front of the valve. This rib 

 appears 2^ to 3 milHmeters from the beak when it is present. Lateral 

 slopes flat or gently convex. 



Dorsal valve flat or gently convex in lateral profile, but broadly 

 sulcate in anterior profile. Median sulcus shallow, usually occupied 

 by a low, indistinct secondary rib near the front of the valve. Region 

 on each side of the sulcus gently convex, but just anterior to the 

 cardinal extremities a prominent depression sets them ofif from the 

 body of the shell. 



Ventral interior : Teeth wide, pedicle collar high and narrow, sup- 

 ported by the median septum which extends nearly to the middle of 

 the valve. The median septum is high, thin, and broadly triangular 

 in profile, the apex of the triangle being located about one fourth 

 the length of the valve from the beak. 



Dorsal interior : The median septum extends nearly to the front 

 margin of the valve and is triangular in profile. Front margin of 

 septum sigmoidal in profile. Apex of septum located at about the 

 middle of the valve. Loop broad, attached to the floor of the valve 

 near the middle. The soft parts of the shell present no new features. 

 The digestive gland is pale yellow in color. The gonads are crescentic 

 in outline and pale yellow in color. 



Type locality. — Station 52 at 14 to 22 fathoms, latitude ig°io'2^" 

 N., longitude 69°2o'55" W. — latitude I9°io'o5" N., longitude 

 69°2i'25" W., attached to worm tubes in association with Thecidellina 

 harretti (Davidson). The above description is based on 6 dried 

 specimens and 26 alcoholic specimens, LT.S.N.M. no. 431003, a-f. 



Holotype. — U.S.N.M. no. 431003. 



Discussion. — There are five known species of Argyrofhcca living 

 in the Atlantic around the West Indies. Three of these species are 

 very small animals and are readily distinguished from A. johnsoni. 

 The other two are rather large for the genus, but this is the only 

 feature in which they resemble A. johnsoni. Argyrotheca bar- 

 rettiana (Davidson) differs from A. johnsoni in color and ribbing 

 pattern. This species is conspicuously marked by scarlet bands in the 

 spaces between the ribs, but the ribs themselves are pale yellow. 



