Description of a New Species of Trilobite
Description of a New Species of Trilobite. By C. D. Walcott, of Trenton Falls, N. Y.
Spherocoryphe robustus, n. sp.
General form subovate, convex; cephalic shield subtriangular, strongly convex; anterior and lateral margins smooth, round edges; posterior lateral angles produced into long subuliform spines; posterior margin nearly transverse; glabella subglobose, constricted at the base, projects beyond the anterior and lateral margins; two minute rudimentary lobes are separated from the anterior lobe by deep furrows each side of the central axis; neck furrows broad and shallow upon the central axis, deepens laterally, and extends to the posterior lateral angles; neck segment a narrow elevated ridge; movable cheeks triangular, convex.
Eyes prominent, subglobose, directed forward and outward from the central eminences of the cheeks; visual surface occupies the outer lateral margins; facial sutures, as far as determined, extend from the posterior third of the lateral margins to the posterior base of the eyes, thence to the top of the eye, curve around the outer margin and then down to the anterior base.
Thorax a little longer than the cephalic shield; axial lobe with ten segments, arching forward, narrows very gradually, posteriorly as wide as the lateral lobes; lateral lobes flattened two thirds the way out, where they abruptly curve downward, narrow slightly posteriorly; pleura straight and transverse, two thirds of their length, where they are geniculated, curving slightly backward, terminate in short mucronate spines.
|Fig. 18, a. Spherocoryphe robustus.
Fig. 18. b. Spherocoryphe robustus; section of glabella.
Pygidium, mesial lobe composed of three segments, anterior segment largely developed, its extemities being produced into long stout spines, incurved toward their points; posterior margin a rounded ridge, curving backwards between the spines, forming a subtriangular depression, upon which, the two posterior segments are situated; entire surface finely granulated; upon the upper surface of the globose glabella the granulations are coarser, so as to be distinguished by the eye.
This species is related to S. granulata (Angelin), and S. salteri (Billings), but differs materially from the descriptions of those species.
Formation and locality: In the upper third of the Trenton Limestone, Trenton Falls, New York.