Clam shrimp are small, freshwater branchiopods that inhabit isolated, ephemeral pools— both natural and anthropogenic. Here we report a new locality for Cyzicus mexicanus (Mexican Clam Shrimp) in Middlesex County, NJ, that represents the first record of this species in New Jersey and a range expansion 120 km north of the nearest documented population. The only member of the genus that has previously been reported in New Jersey is Cyzicus gynecia (Mattox Clam Shrimp). The primary way that Mexican Clam Shrimp is distinguished from its congener Mattox Clam Shrimp is by the presence of individuals possessing male reproductive organs known as claspers. Since the only documented Mattox Clam Shrimp individuals are female, male specimens are indicative of Mexican Clam Shrimp.