The Collaborative International Dictionary
Prosiphon
Prosiphon \Pro*si"phon\, n. [Pref. pro- for + siphon.] (Zo["o]l.) A minute tube found in the protoconch of ammonites, and not connected with the true siphon.
Wiktionary
prosiphon
n. (context zoology English) A minute tube found in the protoconch of ammonites, not connected with the true siphon.