68 



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



Fig. 106 Yoldiella jeffreysi. Siphons as seen from the ventral side 

 of a preserved specimen form Sta. 85, North America Basin. 

 (Scale = 0.1 mm). 



Fig. 107 Yoldiella jeffreysi. Lateral views from the right and left 

 sides of the internal morphology of a specimen from Sta. 85, 

 North America Basin. (Scale = 1.0 mm). For identification of 

 parts see Fig. 34. 



Fig. 108 Yoldiella jeffreysi. Diagrammatic views of the course of 

 the hind gut as seen from the right side to show variations in the 

 configuration. 



pygmaea Munst. as exemplified by U.S. Natl. Mus. No. 

 197285. 



Distributed in the western Atlantic from southern limit of 

 the North America Basin to Guyana, from mid to lower slope 

 depths. Depth range: 1135-2853 m. 



Shell description (Figs. 110 & 111). Shell ovate, not 

 particularly inflated, moderately elongate, slightly inequilat- 

 eral, faint concentric striae particularly close to ventral mar- 

 gin; umbo moderately large; postero-dorsal and antero- 

 dorsal margins slightly convex and slope gently from umbo, 

 anterior margin rounded, anterior limit dorsal to mid hori- 

 zontal plane, dorsal and ventral margins without angulation, J 

 antero-ventral margin smooth curve, postero-ventral margin 

 very slightly sinuous posterior margin not angulated, broadly 

 blunt, posterior limit in mid horizontal plane; hinge moder- 

 ately broad distally, narrows centrally, chevron-shaped teeth 

 robust, close set with ventral arm twice length of dorsal, 

 anterior and posterior plates with up to 7 teeth; ligament 

 amphidetic, moderately large, extends ventral to hinge plate. 



Prodissoconch length: - 287 u,m. Maximum recorded shell 

 length: 3.65 mm. 



This species is similar to Yoldiella ella, however it is less 

 round in outline, shallower dorso-ventrally and less inflated. 

 The ligament is also similar to that of Y. ella as is the hinge 

 plate, however, the latter in Y. ella is more broad and bears 

 one or two more teeth than that in Yoldiella enata. 



Internal morphology (Fig. 112). This is similar to that of 

 Yoldiella ella so much so that it is extremely difficult to 

 distinguish between the two species. Such distinction as there 

 is is a matter of slight difference in proportion. Thus, the 

 anterior adductor muscle is slightly larger, the diameter of the 

 hind gut is slight less and the exhalent siphon is somewhat 

 larger than in Y. ella. Sections of the tightly coiled hindgut 



