A Monograph of the Trilobites of North America: with Coloured Models of the Species

by Jacob Green

[34] From the Greek, for "minute tail."

Cauda attenuata, acuta; corpore valde convexo; costis striatis; parte marginali vix membranacea.

This fine, large caudal termination of an Asaph is in the cabinet of the Albany Institute—and it is a subject of great regret, that all that has yet been discovered relating to this highly interesting trilobite, is to be seen in this fragment.

There are eighteen articulations of the tail and abdomen, which cannot be distinguished from each other. The middle lobe is composed of a series of straight, distinct, parallel articulations, very convex about the middle, so as to form a kind of longitudinal ridge down the back. The costal arches of the lateral lobes are very distinct, and are longitudinally striated or grooved on their upper surface, particularly those near the upper part of the animal. The membranaceous expansion is very narrow along the sides of the body, and forms a sort of hem; below the central portion of the tail it makes a short acute projection, which seems to be supported by a short costal elongation of the middle lobe. Length two inches and a half.

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.

[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.

This interesting species was found in limestone shale, near Rochester, in Munroe County, N. Y.; and is now in the valuable cabinet of the Albany Institute. An accidental fissure of the rock disclosed not only a fine specimen of both the mould and the cast of this animal, but also another individual of the same species in contact with it. From the peculiar attitude which these fossilized animals maintain towards each other, they appear to have been combatants at the very moment when the catastrophe occurred which produced their mineralization. In the Museum of the Garden of Plants at Paris, there is a large specimen of two fossil fish, which are supposed by many to have been destroyed and covered with mineral matter, when one of them was in the very act of swallowing the other. Mr. Bake well, however, who accurately examined this specimen, is of opinion, that the two heads of the fish had been pressed together by the superincumbent weight.