This remarkable organic relic was found near Newport, in the State of New York. It is embedded in black limestone shale, and so exceedingly depressed is this animal, that a very thin lamen of the slate removed from the surface would destroy every vestige of its appearance. I am indebted to my early friend, Professor T. R. Beck, for the use of this valuable petrifaction, which now belongs to the cabinet of the Albany Institute.
Genus Triarthrus. Green.
Body, slightly convex; contractile?
Buckler?
Abdomen, with three articulations, side lobes longitudinal, narrow, and wedge-shaped.
Tail, broad, rounded, without any membranaceous expansion.
The name of this genus is derived from the circumstance, that the abdomen has but three articulations; an organization which is very peculiar. These curious fossil animals are very abundant in the rocks in which they are found; but though I have examined a multitude of specimens from different localities, no vestige of the head or buckler could, on the most minute examination, be discovered. Whether these animals, during their petrifaction, were so contorted or rolled up, as to bring the extremities of the body together, in such a manner as to present the posterior folded part only to the view; or whether the buckler has been destroyed by the process of mineralization, as appears frequently to happen with the asaphs, we are at a loss to determine.
The animal remains which belong to the genus Triarthrus, differ so much in their' form and general characters from all the other trilobites, that we perhaps ought to regard them as forming another race of beings. They are, however, more nearly allied to this family than the Agnosti of Professor Brongniart.
Triarthrus Beckii. Green. Cast No. 34. Fig. 6.
Cauda subrotunda, bipunctata; articulis abdominis tribus, absque lobis lateralibus consuetis, sed lobo arcuato utrinque apposito.