92 



Locality. — Backstairs Passage, near Adelaide, South 

 Australia (Dr. Verco's Coll.). 



Magasella jaffaensis, n. sp., Blochmann. PI. xxvii., 

 figs. 6 to 9. 



Shell in outline almost circular (fig. 6), or from the 

 middle forwards somewhat narrowed (fig. 8), both valves 

 approximately equally deep and equally curved. Commisures 

 in one plane. Growth striae, in places distinct or obsolete. 

 ,Beak short, wide, with moderately sharply-defined edges. 

 Deltidial plates large, joined together. Hole small. 



Number of pores, 170-230. Of three examples, one (fig. 

 8) has the higher number, 212-228 ; both the others, 170-212. 

 Diameter of the round inner opening of the pores, 20-23 /x; 

 of the outer oval opening, 50 by 30 ja. Colour of the shells 

 found dead,, but well preserved, a dirty white. 



The dorsal valve has a moderately-developed hinge pro- 

 cess, and large tooth sockets with comparatively feeble walls. 

 Between these lies a slightly undermined hinge-plate, sunken 

 towards the middle, which extending as a narrow triangle 

 passes over into the strong median septum. This ends 

 abruptly behind the middle with a slightly curved edge. In 

 the posterior half of its course it remains low, in the anterior 

 it rises to a flat surface twice as high as the hinder portion, 

 which on its ventr ally- directed border is split in a furrow- 

 like manner. From the wall of the tooth sockets spring 

 short strong crura, with large slender pointed crural pro- 

 cesses. The descending limbs widen rapidly towards the 

 front, and are applied to the anterior elevated part of the 

 septum, so that the edge of the limb, at first dorsal, then 

 directed centrally, approximately strikes upon the middle of 

 this elevated part of the septum. Towards the front they 

 reach far over beyond the front edge of the septum. This 

 strong widened part of the limb coalesces with the septum, 

 so that it does not project forwards over it, then runs nar- 

 rowing towards the border of the hinge and laterally, bends, 

 still further narrowing, medially again, whereby the two 

 limbs are united by means of a moderately wide bridge. A 

 few small prickles occur at the free anterior border of the 

 part uniting the ascending and descending branch of the 

 limbs. The dorsal and ventral valves are in the posterior 

 part moderately thick; this indicates that the examples are 

 almost or quite mature. 



Dim. — Size of the largest example: Length, 14*6 mm.; 

 width, 13*5 mm. ; thickness, 8 mm. 



Locality. — Cape Jaffa, South Australia, 90 fathoms. 



