TRENTON LIMESTONE. 249 



307. 1. TRINUCLEUS CONCENTRICUS. 



Pl. LXV. Figs. 4 a,b, c ; also pag. 235, and pi. 67. 



Trinucleus. Lhwyd, Phil. Transactions, 169S, Vol. xx, p. 279. 



Trilobites. Bhongniart, Crust, fossiles, 1822, pag. 14.'5, pi. 4, figs. 6, 7 a b c. 



— BiGsBY, Ann. Lye. Nat. Hist. New-York, 1824, Vol. i, pag. 214, pi. 15, fig. 1. 



JVuttainia concentrica. Eaton, Geol. Text-Book, 1832, pag. 128, pi. 1, fig. 2. 

 Cryptolithus tessellatus. Green, Monograph, 1832, pag. 74. 



Trinucleus earactaci. Murchison, Sil. System, 1839, pag. 659, pi. 23, figs. I a b c d. 



Jisaphiu seticornii, and A. cyllarus. Hisinger, Leth. Suecica, Suppl. ii, 1840, pag. 3, pi. 37, figs. 2 and 3. 

 Trinucleus earactaci. Burmeister, 1843, pag. 65, tab. 1, fig. 1. 

 Compare Entomostracitea granulatus, Wahlenberg, Act. Nov. Soc. Sc. Upsalensis, 1821. 



— — Brongniart, Crust, fossiles ( figure after Wahlenberg ). 



Jsaphus granulatus, Dalman, Vet. Acad. Handlingar, 1820, pag. 238, tab. 2, fig. 6. 

 — — Hisinger, Leth. Suecica, pag. 14, pi. 2, fig. 4. 



Buckler semicircular or subcrescent-form, the posterior angles produced into long slender 

 straight spines ; glabella very prominent, finely granulated, produced posteriorly into a 

 short spine ; cheeks prominent, finely granulated ; marginal fillet marked in front by tiiree, 

 four, or five rows of deep rounded pores or punctures ; these rows increase by one or two 

 additional ones on the sides of the shield, and towards the lateral posterior angles are often 

 irregularly scattered. 



The buckler or cephalic shield alone is figured here, as I have no specimen of the thorax 

 or caudal shield from the Trenton limestone, though the buckler is often abundant. I have 

 restored the specific name given by Eaton, adopting the generic name of Lhwyd given 

 by Mt;RCHisoN. There is indeed no reason for a separation on account of the number of 

 rows of pores, as they are variable, and the specimens are more often without the long 

 spines of the buckler than otherwise. The specimen figured by Green, is one before 

 referred to, as coming from the slates of the Hudson-river group, near Waterford, which at 

 that time were regarded as almost non-fossiliferous. Though destitute of the small spines 

 at the posterior angles of the buckler, it is specifically the same as those here presented, 

 and doubtless identical with the figures of Murchison, though more doubt may be 

 entertained as to its identity with those of Wahlenberg and Dalman. 



Fig. 4 a. The cephalic shield of this species, still preserving one of the slender spines from the posterior 

 angle. The posterior spine of the glabella is broken off, though the fracture is not conspicuous. 



Fig. 4 b. Lateral view of the cephalic shield of a smaller specimen. 



Fig 4 e. The cephalic shield of a small specimen, in which the glabella preserves its posterior spine. 

 These specimens present some variety in the number of rows of punctures in the border, 

 and the same is true in many other individuals, showing that this chaiacter is not reliable 

 for specific distinction. 



Position and locality. In the higher subcrystalline portions of the Trenton limestone, and 

 sometimes in the more shaly part of the rock, the bucklers of this trilobite are abundant. 

 The fragile thorax is very rarely preserved, and I do not recollect to have seen one in the 

 limestone in the whole course of my investigations. It is found at Trenton falls, Middleville, 

 Turin, Lowville, Watertown, Glensfalls, and many other localities of this rock. Although 

 more abundant in the Hudson-river group, it is unknown in the intermediate Utica slate. 

 [Palaeontology.] 32 {State Collection.) 



