224 SIXTEENTH EEPORT ON THE CABINET OF NAT. HISTORY. 



tremely prominent ; its base corfstricted by abroad groove, which 

 is more distinct in front, and by which it is strongly separated 

 from the anterior limb. 



In three specimens, we have no evidence of lateral lobes in the 

 position of these parts in ordinar}^ Lichas, though a considerable 

 space is preserved on either side of the anterior lobe ; so that if 

 any such features existed, they were widely separated from that 

 portion of the head. 



The other lobes, whether middle or posterior, are entirely be- 

 hind and on each side of the anterior lobe, and separated by a 

 comparatively broad central space, which extends in a line from 

 the base of the anterior lobe to the occipital furrow, a distance 

 nearl}^ equal to the longitudinal diameter of the anterior lobe^ 

 Each of the posterior lobes consists essentially of three distinct 

 elevations : the inner one is the more rounded and prominent, 

 and is surmounted by two rounded subclavate nodes. Of the 

 lateral portion, the anterior division is subangular, and the po- 

 sterior division less prominent. These features, however, either 

 from accident or other causes, are subject to variation. From the 

 elevated posterior lobes, the surface descends almost vertically 

 to the occipital furrow, which is comparatively shallow. The oc- 

 cipital ring is somewhat broad and little convex : for two-thirds 

 of its width on the anterior side, it is studded with tubercles; 

 and the posterior margin supports a row of strong rounded sub- 

 clavate nodes. 



From two pygidia found in the same association, we obtain the 

 following characters : 



The axis is broad and prominent, but its divisions are not shown. 

 The lateral lobes are about as wide as the axis, marked by 

 three prominent ribs and a less prominent fourth one,^ or divi- 

 sion of the axis ; all terminating in a narrow thickened border, 

 from which proceed, on each side, four long and strong spines, 

 which are themselves spiniferous on their sides, flattened and 

 slightly grooved on the lower surfaces, and tuberculiferous on 

 the upper side. 



The primary tail-spines are sometimes ( perhaps always ) bent 

 backwards, and the secondary spines are often slightly curved. 

 In one example, one of the posterior spines is more than two 

 inches long, and imperfect, having apparently been at least 

 three inches in length. In a^iother fragment, one of the lateral 

 spines still preserves two inches of its length, and, judging 

 from the size where broken, has been at least two inches longer. 



