During the 1973 cruise of the BIOGAS deep-sea program, a series of 83 frames showing a high population density of the isocrinid stalked crinoid Diplocrinus (Annacrinus) wyvillethomsoni was obtained from a depth of 1246 m on the bathyal slope of the Bay of Biscay. The spatial distribution of D. wyvillethomsoni appears to be highly aggregated. Mean density is 0.61 m-² with confidence limits determined as 0.53 and 0.69 m-², ranging up to 8 or 10 specimens m-² on a sea floor with pebbles and rocks. D. wyvillethomsoni forms a parabolic filtration fan with its arms strongly recurved into the current. The distal group of cirri grips pebbles or the sharp upper edges of rocks. This active mode of anchorage contrasts with the passive mode in other genera of isocrinids such as Cenocrinus. The current velocities ranging from 15 to 25 cm s- and the irregular aspect of rocky substrate are likely to affect the spatial distribution of such a rheophilic suspension feeder. The population of D. wyvillethomsoni can produce a crinoidal carbonate sand with a sedimentation rate of 15.9 to 20.7 cm in 100,000 y. With the same density and a higher growth rate, a population of a stouter isocrinid such as Saracrinus superbus could produce a punctual sedimentation of 2 m or more in 10.000 y. The result is compared with possible similar sedimentation rates for mesozoic or paleozic crinoid limestones. [NOT CONTROLLED OCR]