From a gloss on Callimachus Hecale fr.300 Pfeiffer, where, as indicated, the genitive plural form of this toponym (an Attic deme: see further below) occurs. The other genitive plural cited, nhsa/wn [which SOL wrongly gives as the primary headword], occurs in Callimachus' Aetia and (twice) Hymn to Delos.
The gloss criticizes the use of these first-declension uncontracted genitive plural forms. The criticism might be valid in the case of nh=sos "island"; LSJ s.v. calls it heteroclictic. But the primary headword form, contrary to what seems to be assumed here, is the genitive plural not of lower-case "hill," for which both first and second declension forms are attested (see kappa 1963 kolw/nh and kappa 1964 kolwno/s), but of upper-case *Kolw=nai, and thus regular. (If it were from Kolonos (Colonus), as a scholiast on Homer, Odyssey 14.199, supposes, it would indeed be irregular.)
There were two Attic demes of this name (see Whitehead 73 n.30), and the full quotation from the Hecale takes account of this: 'someone brought me to share a hearth out of the other deme K.'.