The A. Micrurus was found in the black fœtid limestone of Trenton Falls, by M. H. Webster, Esq., and by him placed in the rich collection of trilobites in the Albany Institute. The limestone in which this Asaph is embedded, is almost one entire mass of petrifactions. The general aspect of the A. Micrurus is very similar to that of a calymene--but judging from its structure, it could never contract its shell into a spherical figure. Its minute tail, and narrow membranaceous expansion round the terminal edges of the lateral lobes are quite peculiar, and determine it to be an Asaph. Asaphus Wetherilli.[35] _Green._ Cast No. 20. [Footnote 35: I have named this species in compliment to my friend, John P. Wetherill, Esq., whose magnificent cabinet of fossils in the Academy of Natural Sciences of Philadelphia, will ever remain as a monument of his discrimination, enterprise, and liberality.] Clypeo postice arcuato, sulcato; abdominis articulis duodecim; cauda vix membranacea; cute coreacea vix punctata. The contour of this beautiful Asaph is very regularly ovate; unlike most of the remains of this genus, the buckler is still attached to the abdomen, though one of the _cheeks_, and a portion of the _front_ are obscured by the rock in which the animal is imbedded. The cheeks form spherical triangles. The oculiferous tubercles, though a good deal defaced, seem to have been circular and not lunate, as in the A. Caudatus. A raised, curved line passes from and over the eye, between it and the lateral lobe of the abdomen. The central lobe of the back is composed of twelve double joints, and that of the tail of six single articulations; where the epidermis or shell is perfect, all the articulations appear single. The last joint of the tail is longer than in any other of our species. The ribs of the abdomen are rather broad, and have a deep furrow scooped out along their upper surface; their extremities, where they can be discovered, are detached from each other, and terminate in reflected points, like those of the A. Limulurus. The costal arches of the tail are delicately grooved, and terminate in the membrane. The membranaceous expansion round the edge of the tail is very narrow, and appears to form no projection beyond its central part. The whole epidermis is finely marked with granulations. Length one inch and three-fourths--breadth one inch and one-fourth.