Genus Tenth. HEMICRUPTURUS.* Grem. 



Rody contractile. 



Buckler oculiferous and not lobate. 



Abdomen trilobate, with 8 articulations. 



Tail, costal arches covered, middle lobe naked. 



The asaphus expansus of Dal man, and several 

 other known species may be arranged under this 

 genus. 



As Count Rasoumowsky has given no specific ap- 

 pellation to the fossil above alluded to, we propose to 

 call it after his own name, Hemicrupturus Rasoumow- 

 skiL We examined the fine specimen from which 

 our cast is taken in the cabinet of the Baltimore Col- 

 lege, and for this favour we are indebted to the kind- 

 ness of Dr. J. J. Cohen, one of the Professors in that 

 rising institution. 



The following list includes all the genera and spe- 

 cies of the Trilobite Family, hitherto described as 

 far as known to the author. It is taken from De 

 La Beche's Manual of Geology. 



NAMES. 



Calymene Blumenbachii, 

 Macrophthalma, 

 Variolaris, 

 Tristani, 

 Bellatula, 

 Ornata, 

 Verrucosa, 



From three Greek words which signify half-concealed tail. 



