The Cambrian fauna of Massachusetts, characterized by Paradoxides (Hydrocephalus) harlani, is poorly preserved. Better-preserved specimens, occurring within the stratigraphic range of this trilobite in southeastern Newfoundland and Morocco, provide a better understanding of such taxa to widen the scope of correlation. The paradoxidid-bearing Braintree Formation has revealed three trilobite species to add to those recently recorded. They represent Ellipsocephaloidea not previously recognized in this Massachusetts sequence, namely Protoleninae by Hamatolenus (H.) aff. H. (H.) marocanus and H. (Myopsolenus) aff. H. (M.) magnus and Ellipsocephalidae by Holocephalina aff. H. levis, thus strengthening faunal relationships with midshelf Cambrian sequences in Morocco and Spain. Reinterpretations of Agnostida, based on Newfoundland material associated with P. (Hydrocephalus) harlani, indicate that Condylopyge eli and Kiskinella cf. K. cristata signify a stratigraphic position for part of the Massachusetts sequence a little above the first appearance of Ovatoryctocara granulata. Appearance of this latter species is under review as the basal boundary of a global Cambrian stage, and is below the sequence break within the Chamberlain's Brook Formation in Newfoundland marked by the Easter Cove Blister Bed. The problem of differentiating species with numerous variable growth stages is highlighted in the ontogenies and stratigraphic ranges of P. (H.) harlani and P. (Plutonides) haywardi and emphasizes the importance of cephalic morphology in paradoxidid classification. Details of the holotypes of Agraulos quadrangularis and Braintreella rogersi and Czech topotypes of Agraulos ceticephalus supplement generic and specific characters poorly understood, especially those involving proportional differences between tectonically/taphonomically flattened examples and undistorted high-relief specimens.