the Cirri'pede Genus Strrtmeritum. 75 



no doubt due, in some measure, to additional scales being 

 first formed below the eariual and upper lateral valves (s^c 

 under Growth, p. 77), but also to allow suilicieut room for 

 the animal's body. 



Of tiie five rows of scales the three inner series are coni- 

 posed of nearly equal scales, much elongate transversely, and 

 are about as wide as the carinal-latus, upper latus, and 

 scutum, below which valves they are situated, so that the 

 liues of junction of the peduncular scales correspond more or 

 less with those of the capitular plates mentioned. The 

 scales are closely imbricating, the middle series intersecting 

 those ou either side ; and those two series are again in turn 

 intersected by the outer subearinal and subseutal scales, which 

 are in line with the middle series ; the much smaller outer 

 scales simply meet those ou the opposite side of the shell and do 

 not overlap or intersect them in any way. Consequent on this 

 arrangement of the peduncular scales, alternate whorls are 

 formed, one being composed of the large median plates and 

 the siuall outer subearinal and subseutal scales, making in 

 all six rows ; and above and below whorls are formed of the 

 two large lateral plates, making four rows. The structure 

 and relationship to each other of the peduncle-scales, both 

 of the inner and outer surface, is well shown in the specimens 

 depicted in fig. 2 of Plates III. & IV. 



The Shell ivhen complete. — While Darwin erroneously 

 thought that the shell in this genus had a keeled carina and 

 rostrum, he was of the opinion that the lateral valves of the 

 capitulum, as well as the plates of the peduncle, must have 

 been present on both sides of the shell. 



With regard to the lateral capitular valve.^, excepting the 

 carina, decisive proof of their paired nature has been given 

 by Whiteaves, for in the holotype of S. canadensis (1889, 

 p. 190, pi. xxvi. figs. 4, 4 a) the upper lateral series of valves 

 has been either partially or completely broken away, showing 

 underneath the inner surface of the scutum, upper latus, 

 tergum, and eariual latus. In other specimens figured by 

 Fritseh (1887) and H. Woodward (1908) slight displacement 

 of the valves has shown the inner surface of an underlying 

 scutum. It is therefore certain that the whole of the 

 capitular valves were paired, for, in addition to the lateral 

 valves, the valves homologous with the carina can be shown 

 to be })aired, not only in S. pulchcllum, but in S^, haworfhi. 

 'i'he split carina is very clearly shown in the specimen de- 

 scribeil as S. macadami, for fortunately a slight displacement 

 of the upper plate shows part of the iiiner surface of the 

 opposing plate along its entire outer margin : it is a pity that 



