Dr. H. Woodward — M. Cambrian Fossils of the Rockies. 531 



twelve pygidia. There are also fourteen examples of 0. Klotzi, 

 junior, showing the younger stages of this well-preserved species. 



Rominger states that this species attains a length of 11 centimetres 

 and a breadth of 6 centimetres, and that specimens graduate down 

 to as small as 16 millimetres in length. Of the fine series brought 

 home by Mr. Whymper, only two or three examples have the free 

 cheeks attached to the head. This suture-line, separating the free 

 cheek from the fixed cheek and glabella, viras evidently a weak line 

 of union in the hard head-shield of most Trilobites, save in forms 

 like Illcenus, Homalonotiis, etc., in which it is generally more firmly 

 united to the head. 



One is at first struck by the remarkable family likeness between 

 0. Klotzi and 0. BiicM from our own Llandeilo Flags, but after 

 a more careful comparison one observes many important points by 

 •which to distinguish them from one another. In 0. Klotzi the 

 difference between the length and breadth is as 11cm. to 6 cm., 

 ■whilst in 0. Biichi the length is 12|cm. to 10^ cm. in breadth. 

 Both the Mount Stephen and the Builth specimens, as is usually 

 the case with fossils preserved in a slate rock, have undergone 

 considerable compression. 



The comparative length of the head, thorax, and pygidium is 

 3, 3, and 4 cm. respectively, the tail being the longest division of the 

 body. The axis of the body, which is 18 mm. wide at the neck-furrow, 

 diminishes very gradually to 10 mm. and less near the distal 

 extremity, but is not visibly constricted as in 0. Buchi, in which 

 the axis rapidly diminishes from 15 to 5 mm. in the pygidium 

 (see Salter's figures). 



The glabella is nearly straight-sided and not expanded in front, 

 as is usually the case in Ogygia proper. There are three lateral 

 furrows in the glabella, which is rounded in front and separated 

 from the anterior border by a fairly broad rim. There is a well- 

 defined ocular ridge, and the palpebral lobe is narrow. The neck- 

 furrow is smooth, and about 4 mm. deep by 18 mm. broad. 



The fixed cheeks are narrowest at the orbits and expand broadly 

 in front of the eyes, with a compressed semicircular outline around 

 the glabella, and are half as wide as the glabella itself, only con- 

 tracting slightly before uniting with the latero-anterior margin. 

 Behind the orbits the fixed cheeks again expand outwardly at an 

 acute angle, until they reach the ends of the neck-segment. The 

 free cheeks are axe-shaped (the outer cheek border representing 

 the rounded cutting-edge of the axe-blade). The latero-posterior 

 angle of the crescent-like free cheek is produced backwards as 

 a short stout spine which reaches to the third free thoracic segment. 

 Thoracic segments eight in number, but little curved, axial portion 

 without ornament of ridges or tubercles, pleural portion about one- 

 third longer than width of axis ; pleural groove distinct, pleurae 

 slightly curved and pointed at their extremities, and very uniform 

 in size; pygidium deep, but less broad than in 0. Buchi; ribs of 

 tail reaching nearly to the border, with no very distinct smooth or 

 striated margin as in 0. Buchi, only a narrow convex rim against 



