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PACIFIC SCIENCE, Vol. IX, July, 1955 
imens were found which represented varia- 
tions from the normal plan of four buttresses 
per animal. Figure 6a and b illustrate the first 
of these anomalies in which a buttress is 
nearly separated into halves, the halves ap- 
parently connected by only a thin piece of 
ectoderm. All other buttresses on this spec- 
imen were normal. A second anomalous spec- 
imen possessed only two buttresses; these 
were adjacent to one another and were normal 
in all respects. This specimen, however, pos- 
sessed only three swimming plates and only 
the two buttresses just mentioned. Figure 6c 
and d illustrates this specimen. This specimen 
was triangular in cross-section except for the 
buttress missing from the side shown in 
Figure 6d. A third irregular specimen was one 
which possessed the normal four lappets but 
possessed only three buttresses, one being 
completely missing. The last anomaly was a 
specimen which also possessed four lappets, 
but only two buttresses, these being located 
180° apart. This specimen is illustrated in 
Figure 6e and /. 
Carlgren’s T. chuni seems to be very little 
different from T. volitans, the major differ- 
ences being the absence of the buttresses and 
the narrower lappets of his species as com- 
pared with T. volitans. In T. volitans the lap- 
pets, in general, are about as broad as the 
space between any two adjacent lappets, while 
in T. chuni the space between the lappets is 
about twice as wide as the lappets themselves. 
Our knowledge of T. chuni is based on a 
single specimen, 8 mm. long by 4 mm. wide, 
which by the standards of T. volitans is an 
unusually large, robust specimen. Careful 
measurements on the more robust specimens 
of T. volitans from the Pacific have indicated 
that the width relationships of the lappets to 
the space between lappets approaches the 
relationship of these measurements on T. 
chuni , but no specimen has been found whose 
lappets are quite as narrow as Carlgren de- 
scribed for his species. Also no specimen of 
T. volitans has been found which was as in- 
flated as T. chuni and this in itself may account 
for the differences observed. In T. volitans , as 
the specimens become greater in diameter 
(due largely to their state of expansion and 
contraction at the time of fixation), the 
width of the lappets becomes less as com- 
pared to the space between. It may be, there- 
fore, that the presumed difference in relative 
widths of lappets between the two species is 
an artifact of preservation. As far as the 
difference in presence and absence of the 
buttresses between these two species is con- 
cerned it now is strongly suggested that this 
difference also may be an artifact, due in this 
case to a failure in the development of the 
buttresses. I do not choose, at this time, to 
d e f 
Fig. 6. Some aberrant Tetraplatia volitans. a , b, An 
incomplete buttress; c, d , a specimen with three lappets 
and two buttresses; e, f, a specimen with four lappets 
and two complete and two incomplete buttresses. 
synonomize T. chuni with T. volitans , but such 
an act does not seem unwarranted. Another 
matter, which bears on this problem, concerns 
the geographic position from which T. chuni 
was collected (see Fig. 5). Carlgren’s specimen 
came from the beginning of the Benguela 
current off the west coast of the tip of Africa, 
while in the same current, some 14° to the 
