336 
PACIFIC SCIENCE, VoL VIII, July, 1954 
ning just above the distal part of the cirrus 
sac. Along much of this course it is heavily 
supplied with cement glands. It then turns 
backward, narrowing as it receives the com- 
mon oviduct; beyond this it continues for a 
short distance as a narrow, tubular, somewhat 
sinuous Lang’s vesicle. 
Until recently but one species of Plamcera 
with three large teeth in the distal end of the 
cirrus sac was known, namely, P. crosslandi 
Laidlaw (1903: 100), from the coast of British 
East Africa. Laidlaw gave a good description 
of this but did not furnish any figures. Re- 
cently Prudhoe (1952: 175) assigned a spec- 
imen from the Gulf of Aqaba, Red Sea, to 
P. crosslandi on the basis of the presence of 
three large cirrus spines but did not section 
the worm. I recently studied a Plamcera from 
the Galapagos Islands with three large teeth 
in the distal end of the cirrus sac and decided 
it was not identical with P. crosslandi, naming 
it tridentata (Hyman, 1953^/ 188). Both triden- 
tata and pacifica differ from crosslandi in that 
the prostatic vesicle is not bound in common 
with the cirrus sac in the same muscular 
sheath. Further, tridentata lacks a Lang’s vesi- 
cle, having instead a very long and narrow 
vagina recurved on itself, whereas crosslandi 
is described as having a long, thread-like 
Lang’s vesicle, and in pacifica Lang’s vesicle 
is short and tubular. It may be concluded that 
there are several species of Plamcera armed 
with three large teeth at the exit of the cirrus 
sac and that the presence of these teeth is not 
a sufficient basis for species identification. 
The holotype, preserved in alcohol, has 
been deposited in the U. S. National Museum, 
accompanied by the slides of sections of the 
removed copulatory region. 
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