Gill marsupia of Cumberlandia monodonta were observed to contain early developmental stages on 27 October 1982. This occurrence, in conjunction with histological examination of gonads from several specimens, documents the first record for autumnal reproductive behavior in C. monodonta, and lends credence to previous speculation that biannual periodicity occurs in this species. Smith (1976, 1978, 1988) systematically examined gametogenesis and reviewed brooding periodicity within the North American Margaritiferidae. However, information concerning margaritiferid reproductive biology remains sparse. Howard (1915) reported a single vernal brooding female of Cumberlandia monodonta (Say, 1829) and briefly described that individual's glochidia (also see Surber, 1915). These data are augmented by the discovery of an autumnal brooding female C. monodonta and histological examination of gonadal tissues from several preserved specimens collected at different localities. MATERIALS AND METHODS Several individuals of Cumberlandia monodonta (obtained from Meramec River, Times Beach access, 3 km east of Eureka, St. Louis County, Missouri, 27 October 1982) were maintained for several days in aquaria. During this period, one individual discharged large quantities of a mucus-like substance from its excurrent siphon. This material was collected immediately and examined microscopically. Forty additional specimens in collections of the University of Massachusetts at Amherst (UMA), Thomas M. Freitag (TMF), and one of the authors (MEG) were available for histological analysis of gonad activity (Table I). Mussels had been preserved either by fixation in 10% formalin, followed by 70% ethanol, or in alcohol without previous fixation. A portion of the viscera of each specimen was embedded in paraffin and sectioned at 8 ,m. Five sections from each specimen were hydrated to water, stained with Ehrlich's hematoxylin and eosin, dehydrated, and mounted. 1 The Tennessee Cooperative Fishery Research Unit is supported jointly by the U.S. Fish and Wildlife Service, Tennessee Wildlife Resources Agency, and Tennessee Technological University. Additional funding was provided by the Center for the Management, Utilization, and Protection of Water Resources, Tennessee Technological University. TRANS. AM. MICROSC. Soc., 109(4): 407-411. 1990. ? Copyright, 1990, by the American Microscopical Society, Inc. This content downloaded from 157.55.39.189 on Fri, 09 Dec 2016 05:30:12 UTC All use subject to http://about.jstor.org/terms TRANS. AM. MICROSC. SOC.