81 
The original of the head from which our cast was 
made, is in the cabinet of P. A. Browne, Esq., and 
was found by that enterprising Bennet near: Le- 
iat Pa. : 
Genus Trimerus.* Green. 
Body, contractile, tapering, compressed. 
Buckler, pustulous, indistinctly lobate, with only 
two small elevated oculiferous tubercles. 
Abdomen, with thirteen distinct, double niebeillee 
tions—divided into three lobes by a ~~ sie ra) 
nal furrow. , 
Flanks, or lateral Bes: not so broad as the middle | 
lobe. 
Tal, tapering to an obtuse point, pustulous, and 
marked with ten articulations. 
This genus resembles in some respects both the 
Calymene and Dipleura. The form of the buckler, 
the position and structure of the oculiferous tuber- 
cles, and the scarcely lobate divisions of the ab- 
domen, will readily distinguish it from the Caly- 
menes. The articulations of the tail, not. being 
covered with a shelly crust, is a character too ob- 
vious to confound it with the genus Dipleura. There 
is, we think, a beautiful chain of gradations of resem- 
blances, between the Isotelus, Dipleura, Hemicryp- 
turus and Trimerus. The lobes of the abdomen of 
the Isotelus are very distinct, and the articulations 
of the tail are hid by a broad thick shelly crust. The 
From the Greek for ‘ three divisions.’° 
