108 AETICULATA. 



No. 448. Trinucleus concentricus, Eaton. 



Group. In this genus, the pygidium is enlarged at 

 the expense of the thorax. The former is triangular ; 

 and the latter has only six rings. The animal is never 

 found fully rolled up. This specimen is from the Hudson 

 River Group (Lower Silurian), Loraine, N. Y. 



Price, $1.00. 



No, 449. Trinucleus concentricus, Eaton. 



Two specimens. The originals of this cast are from the same locality as the 

 preceding, and are now in the private Geological Cabinet of Mr. Ward. 



Price, $0.60. 

 Nos. 373 — 449. This entire series of Trilobites, — represented in 85 speci- 

 mens, 36 genera and 61 species, — will be furnished, boxed, for $50.00. 



No. 450. Ichnites. 



Tracks, on slab. These tracks appear to have been left by some crustacean 

 animal. They are from the Clinton Group (Upper Silurian), in Herkimer Co., 

 New York. Size. 9x6. Price, $0.80. 



CLASS II. — INSECTA. 



Insects are the most prolific of animals, and are essentially terrestrial 

 or aerial. The body is articulated and chitinous ; the limbs articulated 

 and provided with hooks. 



Arachnidans have only two divisions to their bodies, the cephalo- 

 thorax and abdomen. They have eight legs (the most constant external 

 character), and never more than eight smooth eyes. According to Agas- 

 siz, Insects are superior to Spiders. Owen holds the contrary. 



Insects proper consist of three parts : the head, thorax, and abdo- 

 men. They have thirteen rings ; six legs ; and two or four wings. The 

 modifications of the last furnish the characters by which the Order is 

 divided. 



Thr Myriapods are the only members of the class which have more 

 than eight feet in the perfect state, and in which the abdomen is not dis- 

 tinct from the thorax. The head, also, is not prominently distinct. They 

 are all wingless ; and metamorphic development exhausts itself in the 

 successive acquisition of new segments and legs. They live and grow 

 longer than other Insects. 



