the Hidatsa tribe of the Dakotas; the two languages are the only members of the Missouri Valley Siouan family. The ancestor of Crow-Hidatsa may have constituted the initial split from Proto-Siouan. Crow and Hidatsa are not mutually intelligible, however the two languages share many phonological features, cognates and have similar morphologies and syntax. The split between Crow and Hidatsa may have occurred between 300 and 800 years ago. Phonology Vowels There are five distinct vowels in Crow, which occur either long or short with the exception of the mid vowels. There is also a marginal diphthong ea that only occurs in two native Crow stems: déaxa 'clear' and béaxa 'intermittent'. Consonants Crow has a very sparse consonant inventory, much like many other languages of the Great Plains. Stops are aspirated word-initially, word-finally, when geminated (e.g. [ppʰ]) and when following another stop (e.g. [ptʰ]). Stops in a consonant cluster with h as the initial radical (hp, ht, hk) are unaspirated and lax. Gemination in stops only occurs intervocalically. Intervocalic single, nongeminating stops are lax, unaspirated, and generally voiced. The difference between voiced stops b and d (allophones of m and n) and voiceless stops is hardly discernible when following a fricative, since both are unaspirated and lax. The phoneme k has a palatalized allophone [kʲ] that occurs after i, e, ch and sh, often word-finally. Fricatives are tense; they are only lax when intervocalic. Palatal sh is often voiced intervocalically; s is sometimes voiced intervocalically; x is never voiced. The alveolar fricative /s/ has an optional allophone /h/ in phrase-initial position: sáapa "what" > [háapa] sapée "who" > [hapée] Sonorants voiced /m/ and /n/ have three allophones: w and l intervocalically, b and d word initially and following an obstruent, and m and n in all other conditions. In conservative speech, l is realized as a tapped r, however in general cases it is realized as l, perhaps due in part to the influence of English. Word initially, b is optional for /m/, though b is more commonly realized. The glottal sonorant /h/ assimilates to the nasality of the following segment, but retains its voicelessness. When following i or e or preceding ch, /h/ may be realized as an alveopalatal fricative. Structure Vowel sequences across morpheme boundaries can be quite varied, but short vowels cannot appear alone in the morpheme: V:V (long+short), V:V: (long+long) and diphthong+V (short). Word finally, only a