No. 89.] 113 



XOTE UPON THE TRILOBITES OF THE SHALES OF THE HUDSON- 

 RIVER GROUP L\ THE TOWN OF GEORGIA, VERPXT. 



In the Regents' Tw^elfth Annual Report on the New-York State Cabinet of Na- 

 tural History, I described three species of Trilobites from the shales of the upper 

 part of the Hudson-river group in Georgia, Vermont. I then referred two of these, 

 with some hesitation, to the Genus Olenus (Dalman), and one to Peltura 

 (Milne-Edwards); following the reference to Pdlura {Olsnus) scarab(Boides, as 

 the t3'pe. A further examination of these specimens, and some others, has satisfied 

 me of the impropriety of this reference. Although in many respects approaching 

 to Olenus, these forms differ in some important features; and, in order to avoid 

 cor. fusion, they require a distinct designation. In their general aspect, and in some 

 of the details, these fossils bear a resemblance to Paradoxides; from which they 

 are at once distinguished by the less proportional elongation of the body, the 

 smaller number of articulations of the thorax, the direction of the groove or furrow 

 in the lateral segments, and by the form of the glabella. In the first point they also 

 differ from Olenus, which, though having fewer articulations of the thorax, has a 

 larger number than in our fossils. In their general aspect and expression, these 

 fossils are of what might be termed a "primordial type;" but yet differ from any 

 of the Trilobites in our extreme lower formations sujficiently to be readily dis- 

 tinguished from them. 



The genus Paradoxides was established by Brongniart in 1822 ( Crust, foss- 

 p. 30); and the fossil described by Linne under the name ot Entomolithus para- 

 doxus, as figured and described by Wahlenberg (Act. Soc. Upsal. 1821, pa. 31, 

 pl.l,f. 16), was made the type of the genus under the name Paradoxides tessini. 

 Under the same genus were included P. spinulosus, P. scarabmoides and P. laci- 

 niatus; species described by Wahf.enberg, reproducing the figures of that author, 

 and giving an additional illustration of P. spinulosus. 



In 1826, Dalman, admitting the Genus Paradoxides of Brongniart, never- 

 theless proposed the name Olei^us to include the four first named species; placing 

 P. tessini and P. spinulosus in the first section, and the others in the second sec- 

 tion of the new genus, proposing the generic name of Lichas for the P. laciniatus 

 of Brongn'iart. Subsequently the three species P. spinulosus, P.gibhosus and 

 P.scarabcRoides have been regarded as distinct from Paradoxides, and made 

 the foundation of the Genus Olenus; while the latter of these has more recently 

 been placed under the Genus Peltura. 



In Paradoxides, as now established, we have species with broad lunate cepha- 

 lic shields, with the glabella wider in front : the body or thorax has from sixteen 

 to twenty articulations; the pygidium is narrow, with two to three and even five 

 and eight segments, while the lateral lobes are little developed. 



In Olenus, the cephalic shield is comparatively broader and shorter, the gla- 

 bella narrowing (or not broader) anteriorly : the number of thoracic segments is 

 from fourteen to sixteen; the caudal shield is broader than long and semicircular, 

 the lateral lobes being more developed than in Paradoxides, and both marked by 

 transverse rings or ridges. 



M. Bareande makes the following comparisons between Paradoxides and 

 Olenus : 



" In establishing the family for which we have given Paradoxides as the type, 

 [Senate, No. 89.J 15 



