Thank you very much for your queries about jelly coat formation in amphibian eggs. Although Hasumi (1996) actually seems to be the only paper that has explained the timing of jelly coat formation in any amphibian egg as you suggested, Katagiri (1965) has already made a similar description. As you know, Dr. Katagiri and his colleagues (Hokkaido University) investigated a role in the amphibian jelly coat, but unfortunately, there is little description about the timing of jelly coat formation in amphibian eggs. However, Katagiri (1965) clearly indicated location of eggs and jelly layer formation in the oviduct of the toad Bufo japonicus (p. 635).
Although a purely descriptive study composed of considerable amounts of vague writing, Bulakhova and Berman (2013) described a rough appearance of oviductal changes in female Salamandrella schrenckii (p. 672).
Ouji et al. (1983) examined the development of egg capsules after oviposition in Andrias but did not refer to the egg's jelly coat formation.
In Yamasaki et al. (2013), you can find Japanese description about a rosary of Andrias eggs in Fig. 7 (p. 33, right column, first figure). They explained that the remnant of rosaries was usually expelled from the female's cloacal opening of a spent female. However, I cannot find any description about the timing of jelly coat formation in Andrias eggs.
I am very sorry to say that I am not sure what your statement of "keys to hynobiid larvae or eggs" means. Please let me know concrete examples of these keys.
[P. S.] I have just found a Chinese paper with a brief English abstract (Guo et al., 2005) that may contain descriptions about oviductal changes during the breeding season in the Chinese giant salamander (Andrias davidianus). Although I do not understand Chinese descriptions, the Japanese Kanji-script is similar to the Chinese-script. So, I guess this paper deals with the oviductal changes. If you get any person who can read Chinese, you will know the contents of that paper.
(補足): 諸般の事情で更新が遅れたが、これは2014年5月15日付の回答である。
・Katagiri, C. 1965. The fertilizability of coelomic and oviducal eggs of
the toad, Bufo bufo formosus. Journal of the Faculty of Science, Hokkaido University, Series VI, Zoology 15: 633-643.
・Bulakhova, N. A., and D. I. Berman. 2013. Reproductive system of the Schrenckii salamander (Salamandrella schrenckii, Amphibia, Caudata, Hynobiidae) in spring and fall. Biology Bulletin 40: 664-677.
・Ouji, M., K. Tsuneki, K. Kuwabara, and J. Kobara. 1983. Histological study on the hatching gland cells and the egg capsule in the Japanese giant salamander, Andrias japonicus (Temminck). Zoological Magazine 92: 107-112.
・Yamasaki, H., N. Shimizu, K. Tsuchioka, S. Ueda, T. Takamatsu, K. Sato, and K. Kuwabara. 2013. Practical study for conservation of giant salamander Andrias japonicus in Toyosaka, Higashi-Hiroshima, Japan. Bulletin of the Hiroshima University Museum 5: 29-38. (in Japanese with English abstract)
・Guo, Y., T. Li, and D. Cang. 2005. Advances in research of reproduction physiology of Andrias davidianus. Life Science Research 9: 99-104. (in Chinese with English abstract)
Thank you for your kind reply. Surely, I sent you the local papers, to which you might have no access. I see I understood what a key means (i.e., species identification keys). To my knowledge, actually, there seem to be no complete keys to identify eggs or larvae of Asian hynobiids or salamandrids. However, I know a currently available Japanese paper that depicts rough (indeed poor) sketches of four types of egg sacs (p.89), two types of larvae (p.94), and lentic- and lotic-breeding types (p. 97) of hynobiid salamanders (Hayase and Yamane, 1989) although it has no keys (but for a key-like table, see p.90).
(補足): 諸般の事情で更新が遅れたが、これは2014年5月20日付の回答である。
・Hayase, N., and S. Yamane. 1989. Habitats and reproductive modes in Japanese hynobiid salamanders. Bulletin of the Faculty of Education, Ibaraki University (Natural Science) 38: 85-102. (in Japanese with English abstract)