A 
.passes over 
92 
Locality.—Backstairs Passage, near Adelaide, South 
Australia (Dr. Verco’s Coll.). 
COL MagaseHa jaffaensis, n. sp., Blochmann. Pl. xxvii, J4 
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 striz, 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, 912-228; both the others, 170-212. 
Diameter of the round inner opening of the pores, 20-23 pw; 
of the outer oval opening, 50 by 30 ». 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 com aratively feeble walls. 
Between these lies a slightly undermin d’ hinge-plate, sunken 
towards the middle, which extending as a narrow triangle 
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 ventrally-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. 
