7(] Mr. T. II. Withoiso/i 



the specimen anived too late for illustration in tliis paper, 

 for it shows this character more readily than in the specimen 

 originally iigured as .S. dttricini or in S. haicortld. 



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. pulchdlmn (PI. III. fig. 2). One 

 or two ot" the subcarinal plates can also be seen projecting 

 from beneath the upper scries in the same specimen. 

 Dr. Woodward had the chalk removed from beneath that 

 si)ecimcn, 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 Avas attached to the shell 

 of the ammonite along the margins of the under row of 

 subscutal and carinal plates. 



AVheu comparing S. cj-pansum with S. piilchellian (Withers, 

 1911, p. 29), attention was incidentally drawn to the fact 

 that certain of the specimens figured by Fritsch and of those 

 deseiibed by Woodward, some had the scutum on the right 

 hand and others on the left (see also Pis. III. & IV.). While 

 it was probable from this that the whole of the peduncular 

 ])lates were developed on both sides of the shelly it was not 

 conclusive proof^ since it might have been quite accidental 

 which side of the shell was developed uppermost, in the 

 same way that certain lobsters have the " crushing chela " 

 developed on the right side and others on the left. 



The case of the cirri pede 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 (PI. III. fig. 1 A), 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 cariuo-lateral plates of the peduncle 

 were broken away near the base of the capitulum, and 

 although nothing but chalk ajjpcared to be there, removal of 

 the chalk revealed the presence of the inner surface of the 

 o|)posing plates of the subcarinal and carino-latcral series. 

 Further evidence is aflbrded by the example of S. huworthi 

 (PI. IV. fig. 2), for, although it represents one side of an 

 aluio-t entire shell showing its inner surface, there are in 

 many places preserved in situ the peduncular plates of the 

 other side of the shell, especially tlie series of the carino- 

 latcral plates. Taken together these two specimens conclu- 



