82 
lobes in the Dipleura are scarcely apparent, the 
ribs more numerous; and the covering of the tail 
much smaller. .The lobes of the Hemicrypturus are — 
like those of the Isotelus; but the lateral ones only 
of the tail are covered. In the genus Trimerus the 
lobes are like those of Dipleura, but the ar ticulations 
of the tail are exposed. 
TrimEerus DeLpHinocEePHALus. Green. Cast No. 32, 
ale and Fig. 1. i 
. 2 & 
z j 
Clypeo semilunari, antice compresso; oculis mi- 
nimis, enimentissimis; articulis duplicibus vix lo- 
batis; cauda attenuatas corpore tuberculata. 
In the rich cabinet of American fossils in the 
Albany Institute, there are two fine specimens of this 
species, and I am indebted to that rising and liberal 
institution, for the use of them in the present work. 
Our cast is made from the smaller and more perfect 
specimen of the two. The outline of the buckler | 
forms an irregular semi-ellipse. The front is convex 
between the eyes, and very much depressed anterlor- 
ly, so as to form a sharp edge. The posterior part 
of the buckler is marked with.a transverse groove 
parallel with the articulations of the back. The 
cheeks are small and triangular; the small elevated — 
eye-shaped tubercles being placed in the middle, 
nearly equidistant from each of the angles. ~The 4 
eyes are not reticulated, the summit of each tubercle © 
only presenting a plain oval foramen. The middle 
