_Head_ rounded in front, eyes small, in the temples, very remote. _Abdomen_ with from 9 to 10 articulations, trilobate. _Tail_ expanded as large as the head.[8] [Footnote 8: Some of the species described by Professor Dalman as included in this genus, we think ought to be referred to that of the Isotelus.] _Genus Ninth._ Ampyx. _Body_ very short, contractile. _Buckler_ large, triangular, gibbous; eyes not remarkable. _Abdomen_ short, articulations few (6?), trilobate. _Tail_ expanded, not so large as the head. Professor Dalman has two other genera, which he calls Olenus and Battus, the first is the Paradoxides, and the second the Agnostus of Brongniart. In the 8th Volume of Annales des Sciences Naturelles there is a highly valuable paper "Sur les Trilobites et leurs gisemens," by the Count Rasoumowsky, in which he describes some new trilobites from Russia; the one which he has figured and described as a Calymene[9] from Tzarsko-Selo, undoubtedly belongs to a new genus, very near to the Isotelus. The middle lobe is visible or naked through its whole extent, and the lateral lobes near the tail are covered with a thick cuticular membrane. This genus we propose to call Hemicrupturus, and may be thus characterized. [Footnote 9: The editors of the Annales remark that this is not a Calymene, but that it appears to belong to the genus Asaphus.] _Genus Tenth._ Hemicrupturus.[10]--_Green._ [Footnote 10: From three Greek words which signify _half-concealed tail_.] _Body_ contractile. _Buckler_ oculiferous and not lobate. _Abdomen_ trilobate, with 8 articulations. _Tail_, costal arches covered, middle lobe naked. The Asaphus expansus of Dalman, and several other known species may be arranged under this genus. As Count Rasoumowsky has given no specific appellation to the fossil above alluded to, we propose to call it after his own name, _Hemicrupturus Rasoumowskii_. We examined the fine specimen from which our cast is taken in the cabinet of the Baltimore College, and for this favour we are indebted to the kindness of Dr. J. J. Cohen, one of the Professors in that rising institution. The following list includes _all_ the genera and species 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. AUTHORS. LOCALITIES. Calymene Blumenbachii, Al. Brong. Europe--U. States. Macrophthalma, do. Europe--U. States. Variolaris, do. Europe. Tristani, do. Europe--U. States. Bellatula, Dalman. Europe. Ornata, do. Europe. Verrucosa, do. Europe.