Descviptioii of a 2ieir Genus- and Eleven JSfew Species. 107 



part of eleven thoracic articulations, and part of the head and hypos- 

 toina. 



The glabella appears to be broad, very moderately convex, and sep- 

 parated by a furrow from smaller posterior and lateral lobes. 



The length of eleven thoracic articulations, and the pygidium, is two 

 and six tenths inches; length of thorax, one and four tenths inches; 

 length of pygidium, one and two tenths inches. The estimated length 

 of the head is eight tenths of an inch. The diameter of the middle 

 lobe of the body, at the head, is one and fifteen hundredths inches; at 

 the pygidium, seven tenths of an inch. The lateral lobes, at the 

 pvgidium, have a diameter of eighty-five one-hundredths of an inch. 

 From tliese measurements, we infer a perfect specimen will have a 

 length and breadth each of more than three inches. Middle lobe of 

 the thorax broadl}^ convex; lateral lobes depressed; margins falcate. 



Pygidium transversely, somewhat elliptical; margin deeply lacini- 

 ated; axis marked by two articulations, the anterior one narrow, and 

 the posterior one long and terminating in a point. There is a line 

 marking a partial division of the latter, near the anterior part, into 

 two articulations. The lateral lobes are each composed of three articu- 

 lations; the posterior one somewhat pear-shaped; middle one slighth^ 

 expanded in the central part, and broadl}' rounded below; anterior 

 one more expanded in the middle, and more sharply rounded below. 



The surface strongly pustulose, corresponding punctures showing on 

 the under side of the crust; striated band on the margin of the under 

 side, covering half the lateral lobes. 



This species is remarkable for its large size, and broad, middle, 

 thoracic lobe, which rapidly contracts toward the pygidium. 



The specimen illustrated was found in the upper part of the Cincin- 

 nati Group, near Waj-nesville, Ohio, and is now in the collection of 

 Mr. I. H. Harris, in whose honor we have proposed the specific name. 

 Fragments, of what is supposed to be the same species, have been 

 found near the top of the hills at Cincinnati. 



Pholidops ciNCiNNATiENSis, Hall, 1859. (i3th Re]j. of Regents, etc., 



p. 92.) 



During the past year, Mr. George L. Vallandigham has collected sev- 

 eral specimens of this species, showing both A^alves, and as the ventral 

 valve has never been described we propose now to define it. 



It has about the same size and form of the dorsal valve, but has a 

 little less convexity, and not quite as mau}^ sub-imbricating lines of 

 growth. The apex is directly opposite the apex of the dorsal valve. 

 Immediately in front of the apex, the valve is pierced by a small, round 

 aperture. 



