TRENTON LIMESTONE. 



229 



TRILOBITES OF THE TRENTON LIMESTONE. 



Plates LX. (in part), LXI. - LXV., & LXVI. (in part). 

 40. 2. ILL.'ENUS CRASSICAUDA. 



Pl. LX. Figs. 1 a, b, c, d. 



Entomostracites crasstcauda. Wahleniierg, Nov. Act. R. Soc. Sc. Upsal, 1821, Vol. viii, pag. 27, no. 2, 



tab. 2, fig. 5 & 6; and pag. 294, no. I, tab. 8, fig. & 0. 

 niirnus crasskauda. Dalman, Vet. Acad. Handlingar, 1820, pag. 248, pi. 5, fig. 1 a, h, c. 



— — HisiNGER, Leth. Suecica, 18.37, pag. 10, tab. .3, fig. 4. 



— — PoRTLocK, Geol. Rep. Londonderry, IS43, pag. 3U0, pi. 10, figs. 3 a, 3 6, 4, 5. 

 Illimns trcntonensii. Emmons, Geol. Report, 1S42, pag. 390, fig. 3. 



Compare I//irmis perova/is, Murchison, Sil. System, 1839, pag. 001, pi. 23, fig. 1 a, b. 



Oval with tlie longer axis more or less extended, convex ; buckler large, convex, rotund ; 

 posterior extremities obscure ; eyes prominent, distant from the axis ; maxillary shield 

 small ; thorax distinctly three-lobed, the divisions continuing a sliort distance into bolli the 

 cephalic and caudal shields ; articulations ten, smooth, slender, those of tiie lateral lobes 

 extended ; caudal shield large, semicircular, convex, having the rudiment of a central 

 lobe ; entire surface smooth, or witii fine curving subiinbricating lamellose stria;. 



The general form of this species is variable from its contractility, none of the individuals 

 yet seen being quite perfect. It is distinguished from Isotelus by the number of articula- 

 tions, and by the more rotund and less equal extremities. 



In the rocks of New-York, the cephalic and caudal shields of tin's fossil are frequently 

 found ; but from the delicacy of the articulations of the thorax, they are rarely preserved. 



Fig. 4 a. The caudal shield of a large individual. 



Fig. 4 b. Middle lobe of the cephalic shield, the lateral portions being separated at the sutures. 

 Fig. 4 c. Lateral view of a small entire specimen. 



Fig. 4 d. Dorsal view of the specimen, showing the great width of the middle lobe, and abrupt incurving 

 of the cephaUc shield. 



Position and locality. In the Trenton limestone at Middlcvillc, Watcrtown, Turin (New- 

 York) , Carlisle (Pennsylvania), and in tlie upper pnrt of tiie Birdseye limestone on He la 

 Motte (Vermont). 



