Allen and Greenough's New Latin Grammar for Schools and Colleges
J. B. Greenough, G. L. Kittredge, A. A. Howard, Benj. L. D'Ooge, Ed.

[*] a. Of nouns of the fifth declension, only diēs and rēs are declined throughout. Most want the plural, which is, however, found in the nominative or accusative in aciēs , effigiēs, ēluviēs, faciēs , glaciēs , seriēs, speciēs, spēs .¹

[*] b. The Locative form of this declension ends in -ē. It is found only in certain adverbs and expressions of time:—

[*] c. The fifth declension is closely related to the first, and several nouns have forms of both: as, māteria , -iēs; saevitia , -iēs. The genitive and dative in -ēī are rarely found in these words.

[*] d. Some nouns vary between the fifth and the third declension: as, requiēs , satiēs (also satiās , genitive -ātis), plēbēs (also plēbs, genitive plēbis), famēs, genitive famis , ablative famē.

[*] Note.--In the genitive and dative -ēī (-ĕī) was sometimes contracted into -ei : as, tribūnus plēbei , tribune of the people ( plēbēs ). Genitives in -ī and -ē also occur: as, “ diī ” (Aen. 1.636) , plēbī-scītum, “ aciē ” (B. G. 2.23) . A few examples of the old genitive in -ēs are found (cf. -ās in the first declension, § 43. b). The dative has rarely -ē, and a form in -ī is cited.