tri nuclei dae

pl. [Mod. Lat. trinucle ( us ); Lat. fem. pl. adj. suff. -idœ.] Palæont.: A family of Trilobita (q. v.), with four genera, from the Lower Silurian. The head-shield is enormously developed, with a wide margin, or limb, which is usually perforated by rounded pores; glabella well marked, eyes generally wanting, facial sutures sometimes absent, body-rings reduced to five or six in number, with grooved pleuræ, tail large and sub-triangular.