K. L. Prendergast. 
pillar. On each side of it are deep sockets each of which is bounded by a 
curved plate arising from the side of the cardinal process and making an 
angle with it of about 45°. A very short median septum is present, separat- 
jiig the muscle scars which lie close to the base of the cardinal process. These 
muscle impressions are not dendritic, nor do they show any division into 
anterior and posterior adductors. The brachial impressions are not pre- 
served. Pitting is seen over some parts of the internal surface. 
The dimensions of the shells are shown by the following table: — 
Co-types. 
Conjoined 
valves. 
Pedicle valves. 
Height 
0*75 
1-03 + 
MO 
0-58-f 
Maximum width 
0-87 
1-28 + 
1-41 
0-92 
Length of hinge-line 
0-48 
0-95 
0-95 
0-76 
Variation within the species . — As may be expected in a closely adherent 
species the members of this species vary widely according to the nature 
of the host. The jiedicle valve may be fiat to highly convex (e.g. 10930) ; its 
area, though usually horizontal, may be highly inclined. It seems, too, that 
when the pedicle valve is closely adherent, it tends to assume the ornament- 
ation of its host; thus, in O.S.W.A. 10930 B, where the host is a Orachial 
valve of Spirifer marcoui the pedicle valves exposed are corrugated to fit in 
between the striae. This feature is accentuated by tveathering. 
Comparison u'ith other species . — It is with some trepidation that I have 
distinguish(‘d these specimens from other species of the genus, ])ai-ticularly as 
they had ah’eady been referred to E. complectens (Eth. fil.) by the author 
of that species. Their characters, however, are so distinct, that I have been 
forced to separate them. The specimens are larger and thicker-shelled forms- 
than E. complectens \ they possess relatively large and well-developed car- 
dinal areas, strong teeth and characteristic muscular iinjiression, in all these 
characters being distinct from E. complectens. The mode of attachment can- 
not be regarded as an important difference since, had the shells chosen a 
crinoid as host, it seems probable that the spines would encircle 1he stem, 
and we have as yet an insufficient number of specimens to say that they 
cannot or do not choose cilnoid hosts. 
The species heading of these specimens in Etheridge’s description (1918, 
p. 253) is Strophalosia complectens. but elsewhere in the text and in tlf 
explanation of figures he gives S. complectens. I have assumed therefore 
that the title name was due to a typographical error. 
It is possible that this species is really’ the adherent form of Strophalosia 
etheridgei mihi. The structure of the brachial valves of the two species are 
remarkably similar, the variations seen, such as the higher position of the- 
muscle impressions and the more inclined cardinal proces-i in E. mii>rwooda ■ 
being probably modilications due to the assumption of a fixed habit. The 
external a})pearances of the two species differ only in the presence of spines- 
in E. muirwoodae and this too may be due to the reason noted abo-\'c. 
