230 PALHONTOLOGY OF NEW-YORK. 
294. 3. ILLASNUS TRENTONENSIS. 
Px. LX. Fig. 5. 
Bumastis trentonensis. Emmowns, Geol. Report, pag. 390, fig. 1. 
General form oval-ovate, very convex ; buckler semicircular, rounded and ventricose in 
front, elevated behind ; glabella scarcely distinct, narrow in the middle, but expanding 
before ; eyes approximate, large, form? facial suture making a deep and abrupt sinus at 
the eyes, from whence it turns outward and backward ; central lobe of the thorax broad ; 
segments plane, flat, continuing into the lateral lobes; longitudinal furrows shallow, un- 
defined, slightly continuing into the buckler, and less distinctly into the caudal shield ; 
caudal shield subtriangular, very convex in the middle, and descending abruptly at the 
sides, the margin slightly expanded. Surface marked by fine converging imbricating strie, 
as in other specimens of the genus. 
This rare fossil was obtained by Dr. Emmons, from a boulder near Hogansburgh (N. Y.); 
but from other associated fossils, it clearly belongs to the Trenton limestone. 
The original of the perfect specimen has been lost, and our description is taken from a 
plaster cast. I have placed it under the Genus ILLanus, to which it properly belongs, the 
distinctions between this genus and the Bumastts being scarcely decisive. 
295. 4. ILLASNUS LATIDORSATA (xn. sp.). 
Pu. LX. Figs. 6 a, b. 
General form broadly elliptical ; buckler convex, ventricose, thickened in front; thorax 
with ten narrow articulations ; middle lobe of the thorax very broad ; lateral lobes narrow ; 
surface marked by prominent imbricating lamellose stri. 
The specimen is a fragment, preserving five of the articulations very distinctly, and 
fragments of five others in the stone. The buckler is crushed and broken, so that it cannot 
be perfectly represented. The articulations are very slender, those of the lateral lobes being 
suddenly bent forward just outside of the longitudinal depression. The great width of the 
central lobe (which is four times wider than the lateral lobe) , the well defined longitudinal 
groove, and sudden bending forward of the articulations of the lateral lobes, are distin- 
guishing features, and show it to be clearly distinct from the two preceding species. 
Fig. 6 a. The fragment, natural size. 
Fig. 6 b. Three of the articulations enlarged, showing the lamellose strie. 
Position and locality. In the Trenton limestone near Watertown (New-York ). 
(Cabinet of Mr. ALEXANDER Fitcu.) 
