46 



Fig. 68 Yoldiella inconspicua profundorum. Lateral view from the 

 right side of the internal morphology of a specimen from Sta. 242 

 Argentine Basin. (Scale = 1.0 mm). For identification of the parts 

 see Fig. 34. 



(but broader than in Y. inconspicuous s.s.) short, with up to 7 

 teeth on each side; ligament amphidetic, large, slightly elon- 

 gate, short external secondary extensions of fused perios- 

 tracum on either side of umbo. 



The shell shape of this subspecies while similar to that of Y. 

 inconspicua s.s. is slightly more rounded, in particular the 

 posterior limit of the shell margin is medial instead of 

 supramedial. The hinge plate is broader and the teeth stron- 

 ger in Y. i. profundorum. 



Maximum recorded shell length: 3.31 mm. 



J. A. ALLEN, H.L. SANDERS AND F. HANNAH 

 Shell measurements (mm) & ratios are as follows:- 



Length 



Height 



Width 



H/L 



W/L 



PL/TL 



2.90 



3.31 



2.09 



2.25 



1.25 

 1.47 



0.72 

 0.68 



0.43 

 0.44 



0.52 

 0.52 



Internal morphology (Fig. 68). Very similar to that of Y. 

 inconspicua s.s. and Y. argentinea. In Y. i. profundorum, size 

 for size, the posterior adductor muscle is more elongate than 

 in Y. inconspicua s.s., the palps are slightly smaller and the 

 ridges are broader but not as long and slightly fewer in 

 number (12-14 internal ridges). 



Yoldiella argentinensis (new species) 



Type locality. R.V. Atlantis II, Cruise 60, Sta. 237, 

 Argentine Basin, 11.3.1971, 36°32.6'S, 53°23.0'W, 

 Epibenthic Trawl, 993-1011 m. 



Type specimen, presently housed in the Sanders collection. 

 Woods Hole Oceanographic Institution, Paratypes: in collec- 

 tion held by J. A. Allen. 



Material. 



Cruise Sta Depth No Lat Long 



(m) 



Gear Date 



ARGENTINE BASIN 

 Atlantis II 236 497-518 3 36°27.0'S 

 60 237 993- 26 36°32.6'S 



1011 

 239 1661- 26 36°49.0'S 

 1679 



53°31.6"W ES 11.3.71 

 53°23.0'W ES 11.3.71 



53°15.4'W ES 11.3.71 



Y. argentinensis has only been recorded from Argentine 



Fig. 69 Yoldiella argentinensis. 

 Lateral view of the shells from the 

 right side to show variation in shape; 

 detail of the hinge-plate of a left 

 valve; dorsal view of a shell. 

 Specimens from Sta. 237 Argentine 

 Basin. (Scales = 1.0 mm). 



