Hyalella azteca collected from Douglas Lake, Michigan, have been found to harbor within their intestine a cephaline gregarine. The sporonts are broadly oval-shaped and average twenty microns in length. A circle of deeply-staining granules at the anterior end of the protomerite suggests the presence of an epimerite during an earlier stage. A syzygy consists of two individuals. Cysts averaging thirty microns in diameter are formed in the hindgut. Their devel from the gametocyst through spore duct formation has been observed. Twenty-four hours after a cyst is formed three thickened circular areas representing the basal disks of the spore ducts appear on its surface. Growth of the spore tubes begins at these basal disks and progresses inward towards the center of the cyst. Work is at present being conducted to experimentally complete this life cycle. This form agrees with Kamm’s description of the genus, Gregarina. Since Hyalella azteca is a new host record for any gregarine, this parasite is proposed as a new species, Gregarina Hyalellae. The measurements given above indicate that Gregarina hyalellae is the smallest described gregarine.