43 



Seneca, Ontario County, New York, in dark, slaty 

 limestone, which also contains cubical crystals of 

 iron pyrites. A fortunate blow of the hammer has 

 fractured the rock which contains this trilobite, so 

 neatly, as to present us at the same time with the 

 petrified animal in an almost perfect state, and also 

 with the mould or matrix in which it was imbedded. 

 This arrangement is beautifully illustrated by our 



models. 



% 



GENUS ASAPHUS. Brongniart. 



This genus derives its name from the Greek word 

 Arctpvs obscure. It embraces perhaps more species 

 than any other genus of the family of trilobites. 

 About twenty have already been discovered. Most 

 of them are very characteristic and can easily be de- 

 termined, but as the genus Asaphus, is intermediate 

 between Calymene and Ogygia, it is sometimes a 

 little difficult to decide the genus to which the inos- 

 culating species on each side, belongs. 



In general, the Asaphs may be known by the body 

 being very much depressed, and by the membranaceous 

 development, which extends beyond the lateral lobes. 

 The middle lobe of the abdomen, is rarely more 

 than one-fifth the width of the body. As the abdo- 

 men and tail of the Asaph are the only portions of 

 the animal commonly found entire, the distinctive 

 characters of the genus above given, may generally 

 be ascertained. 



Professor Brongniart remarks, that the ribs of the 

 which correspond in number and position to 



