FOSSILS OF THE HUDSON EIVER GROUP. 107 



face, the concave portion to the shorter, and the shorter lateral margin 

 deflected downwards in some cases (probably the marginal row of plates). 



The surface of the plates is flattened or slightly convex on the sides, 

 and very faintly depressed along the middle, the whole marked by rather 

 closel}^ arranged, annulating, and scaliform transverse lines parallel with 

 the basal or sigmoidal margin, and marking stages of growth. These 

 transverse lines are usually faintest near the apex, and gradually in- 

 crease in width with the increased growth of the plate, but in some cases 

 they are quite irregular in their distances. 



The length from the apex to the basal margin of the plate is usually a 

 little greater than the transverse diameter, and seldom exceeds a six- 

 teenth of an inch, the largest specimens seen not measuring a line in 

 their greatest diameter. 



Formation and locality : In the Hudson River group, at Cincinnati, Ohio. We have 

 detected fragments of a species apparently identical on surfaces of Trenton limestone, 

 from near Trenton Falls, New York, received from C. D. Walcott, Esq. The species 

 is named in honor of U. P. James, of Cincinnati, Ohio. 



Genus CALYMENE, Brong. 

 Calymene Christyi, Hall. 



Plate 4, figs. 13-15. 



Calymene Christyi, Hall; 13th Rept. State Cab., p. 119. 

 Calymene Christyi, Hall ; 15th Rept. State Cab., pi. 10, figs. 2-5. 



"General form elongate ovate, symmetrical; body gibbous, the pygidium 

 equaling the length of the head. Head semicircular, the frontal border 

 expanded and gradually narrowing on the sides, the posterior angles ter- 

 minating in a short, sharp spine. Glabella wide, slightly narrowing 

 toward the front, regularly convex, strongly defined by the dorsal fur- 

 rows, a little concave in the middle of the base ; occipital furrow well 

 defined, nearly straight, and in right line with the cheek furrows ; posterior 

 furrow oblique, defined, but not deep, the middle one nearly rectangular 

 to the axis, while the anterior one is l)ut slightly indented. The pos- 

 terior lobe is much wider than the middle one, and about the same width 

 as the anterior one. Cheeks small. Eyes very prominent. 



" Thorax with thirteen segments ; the axis salient, and a little wider 

 in the middle than the lateral lobes ; the articulations of the latter flat, 

 or slightly curving, for a -little more than one-third their length, when 

 they are suddenly bent downward. 



