246 Proceedings of the Royal Physical Society. 
thickenings extending from the umbones backwards to the 
infero-posterior margin. Close beneath the hinge there is 
a well-marked strengthening rib, which ranges backward 
from the umbo, and is subparallel to the dorsal margin of the 
shell. In some species the thickness of this rib is more than 
double that of any other part of the shell. Adductor impres- 
sions subequal in size, the anterior impression situated close 
to the edge of the shell, and bounded by a slight ridge. 
Posterior adductor somewhat larger, but less strongly marked, 
situated far forward, and close beneath the hinge. 
The pallial sinus has been clearly made out in many 
specimens belonging to at least six species of Allorisma. In 
A. clava it extends to a point about midway between the 
umbo and the posterior margin. 
Sanguinolites striato lamellosus, De Kon.,S. glabrata, Phillips, 
and S. tricostata, Portlock, belong to the Carditide, and have 
only a remote relationship with the present genus. 
The author is indebted to Dr Traquair for the loan of 
specimens. 
XIX. Note on Falco sacer. By J. G. GOODCHILD, 
E40, Mop 
(Read 20th January 1892.) 
[ ABSTRACT. | 
The Saker still appears to be one of the falcons about 
which comparatively little is yet known, as nearly all the 
descriptions of it that have yet been published fail to give its 
specific diagnosis in full. The late Mr John Henry Gurney 
pointed out to the writer some years ago that in all stages of 
plumage this species could be readily distinguished from any 
of the allied forms by the character of the markings on the 
tail feathers, which in F. sacer invariably take the form of 
elliptical spots of cream-colour on each web, and never that 
of continuous bars. To this the writer would add, the colour 
of the legs and feet, which are greenish-blue in the adult 
state—in which respect they stand quite alone amongst the 
