147 



basal edge slightly sinuous, and the rostral margin irregularly toothed. The surface shows deep 

 longitudinal furrows running from the apex to the rostral margin and separating from one 

 another four prominent ridges, the one running along the tergal margin being by far the broadest. 

 The rostru m is patelliform and much larger than the carina ; it might also be compared 

 with a hand, the palm of which is small and the fingers numerous, narrow and strongly curved. 

 The latter are represented by the prominent ridges, which extend to the scutal and carinal 

 maro-ins of the valve and fit between the extremities of the ridges on the surface of scutum 

 and carina. I wished to keep the single specimen intact, and since the margins of the different 

 valves can be made out with certainty only by isolating them, it is quite possible that figure 

 14 of PI. XI is not absolutely correct with regard to the course of these margins — in the 

 main, however, the figure will be found to represent them as they are. 



The basal edge of the rostrum, like that of the carina, is inflected inwards and forms 

 a kind of ledge round the basal aperture of the shell. 



The fixed scutum is broad, its apex obtuse-, it overlaps the scutal triangular part 

 of the fixed tergum with a small radius. An important part of this valve is bent over to the 

 side of the moveable valves, and in consequence the whole valve has somewhat the shape of 

 a cap. The portion of the valve situated at the side of the moveable valves has on its surface 

 several prominent ribs or ridges, running parallel to those on the moveable scutum. They extend 

 further than these, however, and go beyond the basal margin of the moveable scutum. So the 

 inferior parts of these ribs run for a short extent parallel to some of the ribs on the surface 

 of the rostrum, which extend to the basal extremities of the ribs on the moveable scutum. 



The fixed tergum is smaller than the fixed scutum. It consists of three parts: the 

 triangular and distinctly beaked middle part, the scuto-lateral part, which is also triangular 

 and is overlapped partly by the radius of the fixed scutum, and the occludent lateral part which 

 is inflected towards the side of the moveable tergum, the free margin of which runs parallel to 

 the occludent margin of that valve. The surface of the fixed tergum is nearly perfectly smooth, 

 like that of the fixed scutum. 



The membrane (fig. 15 111) representing the basis of the shell is partly seen in the 

 oval basal aperture of the shell ; at the side of the fixed scutum and tergum it still adheres to 

 the outer surface of the object (ibid. ó) to which it has been attached; at the side of the 

 rostrum and carina part of the basal membrane is wanting and in consequence a view of the 

 interior (part of the ovary (ibid. o) etc.) is possible. 



Si ze. The height of the shell is about 5 mm., the distance from the apex of the 

 rostrum to that of the carina 5.6 mm. 



This specimen was collected by H. M. S. "Siboga" at 



Stat. 297. December 27, 1899. Lat. io°39'S., Long. i23°4o'E. Depth 520 m. Bottom: soft 

 grey mud with brown upper layer. 



General remarks. The form of the scutum with its numerous ridges is rather 

 like that of V. nexa Darwin. Yet the present species has the scutum slightly larger and 

 shows a further longitudinal ridge. There seems to be some likeness between the two species 



J 9 



