Generic-level diagnoses are provided for adult males, females, and larvae of the longhorned caddisfly genus Nectopsyche Müller (Trichoptera:Leptoceridae). In addition, seven new Costa Rican species in the gemma species group are described and illustrated: N. exophthalma n. sp., N. monticola n. sp., N. onyx n. sp., N. ortizi n. sp., (also known from Argentina, Brazil, Guyana, Mexico, Panama, Peru, Surinam, and Venezuela), N. tapanti n. sp., N. tuanis n. sp., and N. utleyorum n. sp. The new species are compared with two previously described gemma group species also known from Costa Rica, N. argentata Flint and N. gemmoides Flint, and these, too, are diagnosed and illustrated.