In a recent short note in this Journal (Fraser, 1954) the occurrence was announced, off the entrance to the English Channel, of the solitary form of the salp Ritteriella picteti (Apstein), and seven aggregate forms of R. amboinensis (Apstein), taken by H.M.S. Challenger in 1953. The identification of the aggregate forms as R. amboinensis and not as R.pictetiv/as based, as then stated, on Thompson's (1948) description from a very young specimen of R. picteti which emphasized the similarity of its muscle arrangements to those of Salpa cylindrica and not to Ritteriella amboinensis.

Since this was written, Berner (1954) has described the aggregate form of R. picteti from good specimens found off the west coast of U.S.A., and he has shown that the musculature was in fact not like that of Salpa cylindrica but very similar to Ritteriella amboinensis. Differences were noted in the number of fibres constituting the various body muscles and in the number and arrangement of the oral muscles. A still more recent paper by Yount (1954) includes comparisons of the two forms, based on Berner's characters but also including differences in the length of the endostyle and in body shape (length of anterior and posterior processes, and degree of extension of the gut outside the rest of the body). Yount also goes into greater detail in describing the oral musculature in tie two species.

A re-examination of the specimens taken by H.M.S. Challenger shows them to be in fairly close agreement with both Berner's and Yount's descriptions of R. picteti, but with one or two small differences. The actual number of fibres in the muscles is rather smaller than given by Berner for R. picteti, though the precise figure is difficult to ascertain, and there is no median interruption of the first sphincter muscle in the upper lip which Berner believed to be characteristic, and which Yount accepted.