Hudson-river G»oui>. 2§7 



Olenus ; thorax trilobate, the longitudinal furrows not defined ; segments of the middle 

 lobe moderately broad and flat, those of the lateral lobes grooved along the centre, suddenly 

 bent backwards near the extremity, and pointed : surface markings obliterated. 



The specimen, which is imperfect, preserves five and part of the sixth articulations 

 only, upon the middle and one lateral lobe. The crust appears to have been very thin, 

 and the whole specimen is very much compressed. The elliptical central portion of the 

 buckler, on which the Genus EUiptocephalus is founded, appears to be due in part to the 

 outline of the eyes and the line of the facial suture. This character is not so distinct in the 

 specimen 2 b. The specimen 2 a, though very indistinct, clearly presents the lobate character 

 of the glabella, which is margined in front, as Well as laterally, by a broad coriaceous 

 margin. 



The form of the buckler, its prolongation posteriorly into spines, the form of the 

 glabella, and the character of the* articulations, the grooved lateral segments, and tiieir 

 abrupt bending backwards with pointed extremities, correspond very closely with Asaphus 

 ( Ogyg^c^ ) buchii. The proportional width of the middle lobe, however, is much greater ; 

 and the course of the facial suture is different, so far as can be ascertained. The buckler 

 is more elongated than in Olenus spinulosus, which in some respects it resembles.* 



Fig. 2 a. An imperfect cephalic shield, with several articulations. 



Fig. 2 J. A smaller imperfect cephalic shield. 



Fig. 2 c. A fragment of one of the lateral articulations of the thorax. 



Position and locality. This species was found associated with Calymene beckii, and a few 

 other undetermined fossils, in the dark laminated micaceous slates at Greenwich, Washing- 

 ton county. The position of these slates has already been alluded to ; the particular locality 

 is about three miles northeast of Bald mountain, where the lower limestones are clearly 

 exposed, and upon which these plicated and partially altered slates repose. 



(Cabinet of Prof. Emmons.) 



• This species, with Calymene beckii (Atopa trilineattu )» are those given by Dr. Emmons as the characteristic 

 trilobites of the Taconic system. I cannot admit the Atopa to be distinct from Calymene beckii; and though the 

 other form is doubtless new, it evidently belongs to a lower silurian type. The discovery of a new species in 

 our older rocks, whether among the disturbed or horizontal strata, is not a matter of surprise, for such discoveries 

 are of frequent occurrence. I have already given my own views in regard to the position of these rocks, and I see 

 no reason to change this opinion. Supposing the existence of a system of strata below the Potsdam sandstone, of 

 which we have no proof, we might fairly infer that the wide interval between the deposition of those strata and the 

 Hudson-river group would give us forms of animal life more widely different than these examples offer. The great 

 analogy between the latter species and the succeeding one, which is from strata scarcely disturbed, shows how 

 similar were the forms of two supposed epochs. 



[ PiLiEONTOLOOY.] 33 



