The buckler is subtriangular; on the front there is a figure in high relief, somewhat resembling a _fleur de lis_; or perhaps more, the capital of a Corinthian column. The oculiferous tubercles are rather lower down on the cheeks than usual. The articulations of the abdomen and the tail cannot well be distinguished from each, other; fourteen in all may be easily counted. The middle lobe of the abdomen is nearly equal in breadth throughout. The ribs, or costal arches, are not grooved or bifurcated at their extremities. Length nearly two inches and a half. This beautiful species is in the Philadelphia Museum, where it is labelled as being found in "Hampshire, Virginia." It is mineralized by a dark yellowish limestone. It differs from the C. Blumenbachii, in the form and number of its articulations; in the shape of the head; in having only two flat tuberculous elevations on the front; and in other particulars. In the cabinet of the New York Lyceum, and in that of J. P. Wetherill, Esq. there are some examples of this species from the Miami river, near Cincinnati, Ohio. I have also seen it from Indiana, in a dark coloured limestone, very much distorted. It has never been found at Trenton falls, or at any other locality, as far as my knowledge extends, which yields the true C. Blumenbachii. Calymene Selenecephala.[15] _Green._ Cast No. 3. [Footnote 15: From the Greek for "lunate head."] Clypeo antice rotundato, margine omni valde incrassato; prominentia frontali utrinque trituberosa; corpore tuberculato. The buckler is regularly lunate; the margin is slightly reflected or raised anteriorly, the posterior edge forms a continuous rim, running nearly parallel with the articulations of the abdomen. The front on each side has one large and two small tubercles, near its superior edge. The oculiferous tubercles on the cheeks are on a line with the lowest frontal tubercle. There are fourteen distinct articulations; but as the tail is mutilated and distorted, the total number of joints cannot, from this specimen, be ascertained. The body appears to have been covered with small pustules. These are very evident on the front. Costal arches simple, or not grooved. Length, one inch and three-fourths, breadth of the buckler one inch and one-fourth. This species resembles a little the C. Pulchella of Dalman. The specimen from which the model was taken, is in the possession of Mr. R. Peale, of New York, who willingly lent it for this monograph. He informed me that it was found in the state of New York, but he was unable to name its precise locality. It occurs in a soft ash coloured limestone. No other petrifaction is observable in the fragment of rock which contains it. Calymene Platys.[16] _Green._ Casts No. 4 and 5. [Footnote 16: From a Greek word which signifies Flat,] Clypeo antice rotundato; prominentia frontali utrinque quatuor tuberculis.