Cyclocrinites dactioloides is a marine, calcareous, receptacullitid alga which occurs as a common fossil in the Lower Silurian (Llandoverian Hopkinton Dolomite) of eastern Iowa and northwestern Illinios. The main axis and lateral branches, previously unknown in this species, are described. These internal parts, rarely known in other taxa of cyclocrinitids, were poorly calcified and hence were seldom preserved. The flattened lower parts of the thalli, previously considered resting surfaces, are now shown to result from post mortem, early diagenetic alterations. The lateral branches compare well with similar structures in both present-day dasyclads and in ischaditid receptaculitids and thus bridge the gap between these two separate orders of green algae Includes bibliographical references (p. 14-15) Cyclocrinites dactioloides is a marine, calcareous, receptacullitid alga which occurs as a common fossil in the Lower Silurian (Llandoverian Hopkinton Dolomite) of eastern Iowa and northwestern Illinios. The main axis and lateral branches, previously unknown in this species, are described. These internal parts, rarely known in other taxa of cyclocrinitids, were poorly calcified and hence were seldom preserved. The flattened lower parts of the thalli, previously considered resting surfaces, are now shown to result from post mortem, early diagenetic alterations. The lateral branches compare well with similar structures in both present-day dasyclads and in ischaditid receptaculitids and thus bridge the gap between these two separate orders of green algae Fieldiana series has been published as Geological Series by Field Columbian Museum (1895-1909) and Field Museum of Natural History (1909-1943), and as Fieldiana: Geology by Chicago Natural History Museum (1945-1966) and Field Museum of Natural History (1966-)