1887.] NATURAL SCIENCES OF PHILADELPHIA. 13 



out near the centre ; width of the glabella measured across the 

 upper edge of the palpebral rim is i of the entire diameter of the 

 head at this place. Fixed cheeks are rather broad, the reniform 

 palpebral lobe is margined by a projecting rim, which rim is seen 

 continued under the form of a low rounded ruga extending from 

 the upper angle of the eyes obliquely inward and upward, so as 

 to meet the glabella at the third anterior lateral furrow of it. 

 The occipital furrow and its lateral continuation across the 

 cheeks is well marked. The movable cheeks terminate backward 

 in a long spine reaching down to the third thoracic segment. 



The facial suture line terminates posteriorly near the genal 

 angles, anteriorly it intersects the margin on both sides of the 

 glabella, quite a distance off from it, about perpendicular above 

 the eye rim. 



Thoracic segments in all the specimens, small or large, eight. 

 The gently curved scabre-like ribs abruptly taper backward into 

 a short spinose apex. Their centre bears a rounded broad depres- 

 sion, somewhat diagonal to the axis of the rib, and bordered on 

 both sides by a projecting rounded ruga of which the anterior is. 

 more conspicuous than the posterior. The rachis is moderately 

 convex, gently tapering backward ; its width, compared with the 

 length of the ribs, is as one and one-half to two in j^roportion- 

 The pygidium, as above stated, exceeds the head or thorax 

 slightly in length ; it bears in the larger specimens eleven well- 

 marked annulations, flanked by as many costal expansions Avhich 

 dilate considerably toward the margin, and bear in place of the 

 central depression of the free ribs a rounded central ruga bordered 

 on each side by a furrow ; the edges of the anchylosed ribs are 

 likewise indicated by an elevated rim. 



The curvature of the pygidial ribs is much stronger than on 

 the thorax, and their position to the rachis is more oblique, grad- 

 ually increasing backwards, so that the hinder ribs of the pygidium 

 meet the rachis under an acute angle. The edge of the pygidium 

 is formed by a smooth convex rim, against which the costal rugae 

 abut. 



In the figured specimen the movable cheeks were missing, and 

 have been restored from another specimen with the head perfect. 

 Ogygia serrata. nov. sp Pi. i, figs. 2, 2a. , 



There are four complete specimens in the collection, besides 

 numerous fragmental ones ; nearly all are about equal in size ; the 



