A caryophyllaeid cestode, Isoglaridacris agminis sp. n., is described from the lake chubsucker, Erimyzon sucetta (Lacepede). A low number of testes occurring in one dorsal and one ventral row separates I. agminis from others of the genus. A table comparing the species of Isoglaridacris is presented. Four species of Isoglaridacris are known (Table I). All of these have been described from the western and northern United States. The following is the first description of a species of Isoglaridacris from the southeastern United States. MATERIALS AND METHODS Host fish were collected with 10and 50-ft seines, backpack shocker, monofilament gill nets, and trammel nets. They were held alive until all were examined within 24 hr of capture. Cestodes were fixed in hot 5% formalin. Paraffin sections of 12 ,u thickness were prepared and stained with hematoxylin and eosin; whole mounts were stained with Semichon's carmine or Semichon's carmine with a fast-green counterstain. Sections and whole specimens were mounted in Permount. Measurements were based on relaxed, unflattened specimens. Measurements of testes and of vitellaria follow Mackiewicz (1963). Ten eggs were measured from the uterus of each specimen. Measurements are in microns unless otherwise indicated, with range in parentheses. Drawings were made with the aid of a Bausch and Lomb Trisymplex microprojector and a camera lucida. Comparative material (all USNM Helm. Coll.) consisted of a paralectotype of I. hexacotyle Mackiewicz (4793), the holotype of I. longus Frederickson and Ulmer (60302), and paratypes of I. bulbocirrus Mackiewicz (39288) and I. folius Frederickson and Ulmer (60301). Isoglaridacris agminis sp. n. (Figs. 1-5) Host and locality: Lake chubsucker, Erimyzon sucetta (Lacepede), Uphapee Creek, 4 miles northeast of Tuskegee, Macon County, Alabama. Habitat: Intestine, loosely attached. Specimens studied: 22 (10 measured). Type specimens: Holotype and two paratypes, Received for publication 14 March 1972. * Supported by the Southeastern Cooperative Fish Disease Project (in part by Sport Fish Restoration funds and Rockefeller Project RF65061). USNM Helm. Coll. Nos. 72235, 72236; paratypes in authors' collections. Description Gravid adults 5.518 mm (3.770 to 7.730) in length by 575 (470 to 780) in greatest width. Outer longitudinal muscles poorly developed. Wedge-shaped scolex with 3 pairs of shallow loculi. Neck of moderate length. Length from tip of scolex to vitellaria 1.968 mm (1.390 to 2.910). Testes, numbering 28 to 40, located in 1 dorsal and 1 ventral layer. Testes 166 (101 to 221) by 134 (91 to 188), beginning 1.994 mm (1.420 to 2.930) from tip of scolex and extending to cirrus pouch; not extending to anterior limit of preovarian vitellaria. Genital aperture 901 (680 to 1,290) from posterior. Cirrus unarmed, eversible pouch, oblong, 138 (120 to 162) by 118 (85 to 138). External seminal vesicle 144 (137 to 147) in length by 75 (73 to 77) in maximum width. Ovary elongated, inverted, A-shaped with open apex, arms 580 (420 to 840) in length. Vagina lacking seminal receptacle. Vitellaria 54 (34 to 66) by 34 (32 to 43), beginning 1.160 (630 to 2.230) from scolex and extending to ovary; postovarian vitellaria present, not continuous with preovarian vitellaria. Eight pairs of osmoregulatory canals in testicular portion of body. Eggs operculate, shell smooth, 45 (34 to 66) by 34 (32 to 43).