[27] Derived from Selene, moon, and ouros, tail.
Cauda semilunari; costis angustis, valde distinctis; abdominis articulis duodecim; corpore convexo.
I am indebted to Professor Eaton, for two specimens of this very interesting species. In his Geological Text Book, he thus describes it: "Tail crescent-form, or concavo-convex, with the convex side forward, upon which the post abdomen terminates: abdomen contains about 12 articulations, with an abrupt termination equal in breadth to one-fourth of the length of the transverse lunate tail; the articulations of the side lobes gradually incline towards the axis of the body, until the last pair terminate at the tail. Found in transition limestone at Glenn's Falls, and Becroft's mountain, near Hudson. I have a specimen from Becroft's mountain, with part of the original covering of the animal remaining."
When we first noticed the remarkable lunate appearance of the tail of this Asaph, we supposed that it was occasioned by some accident, but there seems no doubt that this conformation is natural. In our specimens of this species, which are not however perfect, the articulations of the abdomen do not exceed 8 in number. The representation of this animal remain given by Mr. Eaton, plate 1, figure 1, is exceedingly inaccurate; it will confuse rather than illustrate the subject. Our cast and the drawing, we believe, are taken from the same specimen, which was kindly loaned by Mr. Eaton for this work. It is but justice to the amiable, industrious, and indefatigable author of the Geological Text Book to remark, that he regrets as much as any one, the insufficiency of his figures of the trilobites, to give any correct idea of the fossils they are intended to represent.
In the cabinet of the Albany Institute there are a number of specimens of the A. Selenurus. One of our models represents the natural mould made by the animal in the rock; the other is an impression taken from it, in order to exhibit the animal in a more satisfactory manner.
Asaphus Limulurus.[28] Green. Cast No. 16.
[28] From two Greek words, which signify "Limulus tailed."
Cauda longa, spina munita sicut in Limulo; costis abdominis in spinis retrorsum flexis, desinentibus.
It is very much to be regretted that the abdomen and caudal end only of this remarkable Asaph have hitherto been discovered; it is, however, exceedingly gratifying that the fragment still remains in so perfect a state. It forms a part of the magnificent cabinet of organic remains belonging to J. P. Wetherill, Esq., now deposited in the Academy of Natural Sciences, of Philadelphia.
Dr. J. J. Cohen discovered a small specimen of this species at Lockport, New York, which he has presented to the Athenæum, in Baltimore.