Notobryon clavigerum Baba, 1937: 168, figures 4–6; Baba, 1949: 92, plate 37, figure 134, text figure 116. Nakano, 2004: 218, top three photos.

No specimens of N. clavigerum Baba, 1937 have been studied in the present paper because types were not traceable. This species was originally described by Baba (1937) from a single specimen of 80 mm in length collected in Japan, Sagami Bay, Amadaiba, in July 1935. The general shape of the body and most of the external and internal features are very similar to the two previously described species but Baba claimed that there are enough differences to describe N. clavigerum as a different species. Thus, Baba stated that in N. clavigerum the rhinophoral sheaths have a longitudinal crest not only along the posterior margin but also along the anterior margin that ends distally in a wavy margin. Another interesting difference is that the dorsolateral lobes have smooth edges except at the tip, which stands recurved having a row of small claw-like papillae, five on the anterior and three on the posterior lobes, respectively. Moreover, in N. clavigerum, the posterior end is long and has a lower crest on the middle line than in the previously described species. The remaining external and internal features described by Baba (1937) are very similar to N. wardi and N. bijecurum except for the description of hermaphroditic glands consisting of nine separates lobes and the presence of only six gastric plates. The reproductive system is not described.