A new species of Proteocephalus inhabiting the eleotridid estuarine fish Gobiomorus maculatus is described from Chamela Bay, Jalisco State, Mexico. The new species and P. pugetensis are nearly identical in strobila length, presence of a vestigial apical organ, having vaginae only anterior to the cirrus sac, an average of 4-7 uterine diverticula per proglottis, and a ratio of cirrus sac length to proglottis width averaging approximately 1:4. Proteocephalus pugetensis differs from the new species by having an average of 35 rather than 68 testes per proglottis, vitelline follicles terminating posteriorly at the level of the anterior margin of the ovary rather than at the level of the posterior margin, and equatorial genital pores rather than genital pores located in the anterior 1/4 of the proglottis. Finally, Proteocephalus pugetensis occurs from estuarine habitats along the Pacific coast of the United States; the new species was collected from an estuarine habitat on the Pacific coast of México.