Sentence:  The "rostrum" is the anterior extension of the carapace between the eyes. It ends in a more or less acute tip, or <WSD>acumen</WSD>, and may have a lateral spine on each side or bear a longitudinal keel (carina) on the dorsal surface. 
Meaning of the word marked with <WSD> tags:  A bony, often sharp, protuberance, especially that of the ischium.