FEATURES of the Icelandic calendar to be compared with the 364DY Jewish ones:
1. Specific to the 364DY Jewish calendars and already noticed in comparison with the Icelandic calendar:
1.1. 364 days per year: common feature of a great number of calendars (one of the two points of similarity noticed so far).
1.2. 12 months containing 30 days: common feature of the most (whereas not all) of the Jewish 364DY calendars (another one of the two points of similarity noticed so far).
2. Features specific to many 2nd Temple Jewish calendars but not necessarily 364DY ones:
2.3. Strict symmetry between the two halves of the year: cf. Icelandic misseri ("semester") as a more important chronological unit than "year".
2.4. Beginning of the year (in fact, two beginnings of the symmetrical year, in the spring and in the autumn) in the months whose middle is close to an equinox.
2.5. All the months have an equal length of 30 days (thus in the most of the 364DY-calendars but also in many other calendars, eg., the Old Egyptian with the movable Sothic year): in the Icelandic calendar, this looks abnormal against the lunar months in its alleged Germanic background, where the month lengths were harmonised, in some way, with the lunations.
3. MOST IMPORTANT: specific 364DY-calendar features shared by the Icelandic calendar:
3.6. Beginning of the day (nychtemeron) at the sunrise throughout the year (thus in the 12th and 13th cent.: Bókarbót, Grágás, whereas later only in the summer period, with counting from sundown during the winter): another common feature of the Jewish 364DY calendars (so far passed unnoticed). It is VERY impractical in the polar lands, and this is why it was later abolished for the winter! The German peoples traditionally started the new day on the sunset (cf. Tacitus, Germania, 11: Nec dierum numerum, ut nos, sed noctium computant. Sic constituunt, sic condicunt:
nox ducere diem videtur).
3.7. In date definition, the counting of the weeks is prevailing over the counting of the months: specific to the 364DY-calendars having symmetrical substructures formed by long week-cycles. Most of them are seven-pentecontad ones (that is, each year contains seven 49-day cycles plus three additional weeks); 3 Baruch and 2 Enoch calendars, however, contain different variants of 4-part symmetry (2 semesters subdivided into two halves) similar to the Icelandic year (where each misseri is clearly subdivided into two halves).
3.8. aukanætur ("additional (four) nights", that is, additional four days) to 12 months (12 х 30 = 360, and so, four days are to be added) introduced into the third month of summer (Sólmánuður "month of Sol(stice)"): the exact correspondence in the Second Temple Jewish 364DY-calendar preserved within Falasha's liturgical book The Liturgy of the Seventh Sabbath. I think, however, that this feature goes back to the Book of Tobit and originated from a Jewish Second Temple milieu in Egypt (s. my paper on The Liturgy of the Seventh Sabbath). There is a difference between this Tobit-mode intercalation and that of the Icelandic calendar: in Tobit and, presumably, in the The Liturgy of the Seventh Sabbath, the four days are introduced within the days of the Pentecost (which falls always within the third month), whereas, in the Icelandic calendar, they are added at the end of the month. This difference would have appeared when the calendar ceased to be used for liturgical purposes. Anyway, this allegedly the most striking difference between the Icelandic and the Jewish 364DY-calendars turns out not to be striking at all.
3.9. sumarauki ("summer addition/increase": an intercalation week, the 53th one, added once per seven years for catching up the 365-day solar year); added immediately after the aukanætur. Traditional accounts attribute this intercalation to Þorsteinn Surtr's calendrical reform in 955. This is, however, the most natural and most ancient way of intercalation for such calendars; it is the place of intercalation that matters. The same place of the one-week intercalation is provided in the calendar of The Liturgy of the Seventh Sabbath. For me, it is not to be taken for sure that Þorsteinn Surtr has invented anything and not simply recalled...
3.10. The weekday of the beginning of the calendar: it is a very important constant for the 364DY-calendars. In the Jewish 364-DY calendars it is either Wednesday (mostly) or Sunday (much rarely), but the Sumardagurinn fyrsti ("First day of summer") is always Thursday. The problem is revealed through the discrepancy between the two alternative traditions concerning the date of the Fyrsti vetrardagur ("First day of winter"): either Saturday (thus in Grágás and early calendrical texts) or Friday (thus in farmer customs which were very strong during the centuries but attested to in a written source for the first time in 1508). Already G. Björnsson 1910 and N. Beckman 1914 supposed that Saturday resulted from the 12th-cent. calendrical reform, whereas Friday is the original weekday (their reasoning could be easily enforced with other arguments). 1.VII Saturday corresponds to 1.I Thursday, whereas 1.VII Friday corresponds to 1.I Wednesday. QED.
The Old Icelandic calendar preserves a Jewish scheme of the Second Temple period where 1.I was Wednesday, and the four additional days were introduced as an epagomenon in the third month. The closest analogue among the known calendars is that of the Liturgy of the Seventh Sabbath, save that the latter begins on Sunday and not on Wednesday.
1. The Old Icelandic "pagan" names of the weekdays follow the common Latin pattern (mutatis mutandis, e.g., translating "Venus" as "Freyja") adopted throughout the Latin Christianity.
2. Time rekoning in eyktir ("octants" = 1/8 of 24 hours, ca. 3 hours): absolutely unknown among the German peoples (cf. Nilssen, Primitive Time Reckoning, 1920) but corresponds to Roman army's vigiliae and, consequently, to the canonical hours of the Christian liturgy!
ERGO: my hypthesis about papar's influence.
Taking into account my reconstruction of the 7th-century Celtic calendar where the Easter was always falling on Sunday and, in the same time, on 14 Nisan (I concluded that this calendar was 364DY, too; Lourié 2006).