76 Mr. T. H. Withers on 
the specimen arrived too late for illustration in this paper, 
for it shows this character more readily than in the specimen 
originally figured as S. darwini or in S. haworthi. 
As to the peduncular plates, the only evidence so far given 
of an opposing series is that the under row of subscutal 
plates are to be seen projecting from beneath the upper row 
in the figured example of S. pulchedlum (PI. ILI. fig. 2). One 
or two of the subcarmal plates can also be seen projecting 
from beneath the upper series in the same specimen. 
Dr. Woodward had the chalk removed from beneath that 
specimen, and did not find any evidence of an opposing 
series of the three median rows of peduncle-plates. He 
thereupon suggested that they were not developed on the 
under side of the peduncle, which was attached to the shell 
of the ammonite along the margins of the under row of 
subscutal and carinal plates. 
When comparing S. eapansum with S. pulchellum (Withers, 
1911, p. 29), attention was incidentally drawn to the fact 
that certain of the specimens figured by Fritsch and of those 
described by Woodward, some had the scutum on the right 
hand and others on the left (see also Pls. HI.& 1V.). While 
it was probable from this that the whole of the peduncular 
plates were developed on both sides of the shell, it was not 
conclusive proof, since it might have been quite accidental 
which side of the shell was developed uppermost, in thie 
same way that certain lobsters have the “crushing chela” 
developed on the right side and others on the left. 
The case of the cirripede Verruca might also have been 
mentioned, for in that genus it seems to be quite a chance 
whether the movable scutum and tergum are developed on 
the right or left side of the shell. 
A detailed examination of one of the specimens described 
as S. darwini (Pl. III. fig. 1A), not figured by Dr. H. 
Woodward, was rewarded by the discovery that the plates of 
the peduncle were actually present on both sides. Some 
of the subcarinal and carimo-lateral plates of the peduncle 
were broken away near the base of the capitulum, and 
although nothing but chalk appeared to be there, removal of 
the chalk revealed the presence of the inner surface of the 
opposing plates of the subcarinal and carino-lateral series. 
Further evidence is afforded by the example of S. haworthi 
(Pl. IV. fig. 2), for, although it represents one side of an 
almost entire shell showing its inner surface, there are in 
many places preserved im situ the peduncular plates of the 
other side of the shell, especially the series of the carino- 
lateral plates. Taken together these two specimens conclu- 
