No. 186.] 61 



Another fragment, whicli is apparently of the same species, preserves 

 eleven articulations of the thorax and the pygidium. The upper articulations 

 are imperfect at their extremities ; the last one is bent abruptly downwards, 

 and terminates in a long spine on each side reaching below the pygidium. 

 Pygidium semioval ; the axis marked by four annulations, the two upper 

 of which are faintly indicated in the lateral lobes. 



This species differs from the preceding in its proportionally narrower 

 form, the relative proportions of the parts of the bead, and the short acute 

 posterior spines. The comparative width of the middle and lateral lobes of 

 the thorax is a very distinguishing feature. 



Geological position. In the shales of the upper part of the Hudson-river 

 group. 



Peltura (Olenus) holopyga ( n. s.). 



Entire form elongate subelliptica-1, having a length of about twice and a 

 half the width. Head somewhat semielliptical ; the posterior angles pro- 

 duced in long spines. Glabella strongly lobed, its length a little greater 

 than its greatest breadth ; the entire breadth of the head, when entire, 

 being about twice as great as the length. Hypostoma wider than long. 

 Thorax with eleven articulations ; the middle lobe prominent, and about 

 twice as wide as the lateral lobes ; the articulations strong, rounded 

 above, and each one marked in the centre by a node (or the base of a 

 spine which has been broken off in the specimens examined ). Articula- 

 tions of the lateral lobes short (the extremities of the upper ones broken 

 off in the specimen) ; the lower ones bending abruptly downwards, and 

 terminating in spiniform processes, the last pair being prolonged much 

 beyond the extremity of the pygidium. 

 Pygidium longitudinally semielliptical ; the middle lobe marked by three 

 annulations, and a fourth obscure one above the terminal lobe : lateral 

 lobes flat and plain, the exterior margin apparently free from ornament 

 or inequality. 



The specimen from which the description and figure have been made is 

 imperfect, in the absence of the cheeks with the posterior spines and frontal 

 limb. These parts, with the hypostoma attached, lie upon the stone a little 

 in advance and turned to one side of the head of the specimen, and have 

 been drawn in their proper relations, but not attached to the head. That 

 this portion of a tiilobite belongs to the one figured, can scarcely admit of 

 doubt ; but in the absence of an entire head, which would warrant the 

 restoration, I have given the figure as it occurs on the stone, with merely 

 a change of the relation of the two parts. It is not proved, from this spe- 

 cimen, that the third articulation from the head may not have extended 

 beyond the others, as shown in the two preceding species. 



This species appears to belong to the Genus Peltura, taking the figures 

 of Olenus {Peltura) scarahoeoides as the type of the genus*. Our specimen 



* This species, the Entomostracites scarab ceoides of Wahlenberg, 1821 {scarabce- 

 orum vcl aliorum vaginipennium animale vestigia : Beomel inAct.Litt.Up3alil729)j 



