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 geologist near Le- 

 highton, Pa. 



GENIJS TRIMERUS.* Green. 



Body, contractile, tapering, compressed. 



Buckler, pustulous, indistinctly lobate, with only 

 two small elevated oculiferous tubercles. 



Abdomen, with thirteen distinct, double articula- 

 tions divided into three lobes by a slight longitudi- 

 nal furrow. 



Flanks, or lateral lobes, not so broad as the middle 

 lobe. 



Tail, tapering to an obtuse point, pustulous, and 

 marked with ten articulations. 



This genu$ resembles in some respects both the 

 Calymene and Dipleura. The form of the buckler, 

 the position a'nd 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." 



