1. Data concerning reproductive behavior and development in the spider crab, Libinia emarginata (L.) are recorded. Ovigerous females were collected from early June to early September. Females are apparently able to produce at least 3-4 consecutive broods of 25 days development each during a breeding season. 2. Two distinct reproductive behavior patterns are associated with the release of zoea on the 25th day of development, i.e., mating and obstetrical behavior. These male-female associations are stereotyped behaviors. The position of the bodies of the male and female differ in the two behavior patterns. 3. The predictability of onset of these behaviors and the specificity of the patterns suggest their possible initiation by pheromone(s).