Crossword-Solution: RISSOA 6 letters, 1 clue 🏆 scrabble score: 6

There are also shells of the genus _ Rissoa_ (of the subgenus _Hydrobia_), and a little _ Cardium_ of the subgenus _Protocardium,_ in these marine beds, together with _Cypris._ Some of the cypris-bearing shales are strangely contorted and broken up, at the west end of the Isle of Purbeck.

Hydrobia marginata.* (* This shell is said to have a sub-spiral operculum (not a concentric one, as in Paludina), and therefore to be referable to the Hydrobia, a sub-genus of Rissoa.

Blake records from this pit the following fossils{93a}:—Belemnites nitidus, Ammonites serratus, Rissoa mosensis, Avicula ædiligensis, Cyprina cyreneformis, Ostrea deltoides, Lima ædilignensis, Thracia depressa, Arca, Serpula tetragona.

They are of world-wide distribution; but _Solarium_ and _Phorus_ are tropical; while _Lacuna_, _Skenea_, and most species of _Rissoa_ are Northern.

The power of suspension by a thread is also possessed by certain of the _Cyclostomatidae_, by some _Cerithidea_, several _Rissoa_ and other marine genera, prominent among which is _Litiopa bombyx_, whose name expresses its power of anchoring itself to the Sargasso weed by a silken thread of mucus.