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 articulations 

 of the tail are exposed. 



TRIMERUS DELPHINOCEPHALUS. Green. Cast No. 32, 

 and Fig. 1. 



Clypeo semilunari, antice compresso; oculis mi- 

 nimis, enimentissimis; articulis duplicibus vix lo- 

 batis; cauda attenuata; 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 anterior- 

 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 

 eyes are not reticulated, the summit of each tubercle 

 only presenting a plain oval foramen. The middle 



