274 
PROCEEDINGS OP THE ACADEMY OF 
[1889. 
NOTES ON THE ANATOMY OF PHOIAS (BAENEA) COSTATA LINNE, 
AND ZIKPH.ffiA CKISPATA LINNE. 
BY W. H. DALL. 
In P. costata thè mantle is entirely closed, except for thè passage 
of thè foot. The siphons of thè specimen (contraeteci in alcohol) 
combined in a single envelope with distinct terminal orifices, are 
little shorter than thè whole of thè rest of thè body ; their surface is 
finely circularly wrinkled, they bave no epidermidal coat and no 
terminal coriaceous appendages. Tlie papillse around thè two orifices 
are small and inconspicuous. The mantle margin is simple; thè 
mediati line of thè connective tissne joining its edges is marked off 
by a pair of not very prominent raphes. The aperture for thè foot 
is ovai, about one qnarter as long as thè shell. About it is a smooth, 
thick membrane extending laterally to a raised papillose ridge, thè 
anterior prolongation of either raphe, which separates it by a narrow 
space from thè much tliinner simple margin of thè mantle, which is 
continuous with thè epidermis. The tissne of which this encircling 
membrane is composed is thick ; within thè aperture, extending a 
little behind it, on each side is a sort of curtain wliose office 
apparently might he to dose around thè foot and prevent theinflux 
of sancì or mud. The anterior ends of these curtains do not reach 
as far forward (by a distance about equal to a third of their whole 
length) as thè anterior comrnissure of thè pedal opening. On open- 
ing thè mantle-cavity we are first struck by thè immense size of thè 
labial palps; thè anterior or external palpus is aclnate throughout 
thè greater part of its extent upon thè inner surface of thè mantle ; 
only a small anterior border and its lateral tips being free. It is 
radiately striate, with transverse dose-set lamellie on its free mar- 
gin. The lower or posterior jialpus is very thick and cellular, with 
a lamellar gill-like surface internally, but smooth on its outer face. 
It is produced laterally into long slender points which extend back- 
ward further than thè pedal opening. It is not muscular, at least 
to any great extent, and is supported by thè apophyses proceeding 
from under thè beaks of thè shell ; these processes are buried in its 
substance, though their distai margins also penetrate thè visceral 
mass internally for a short distance beyond thè palpi. The foot 
may be said to form thè ventral face of thè whole visceral mass ; it is 
flattened, laterally carinated and terminates behind in an acute free 
