PalcBozoic Fossils. 399 



lesti'ict. Lake, may be the internal cast of the same form which I 

 have defined as P. acacia fi'om impressions of the external sur- 

 face. 



One nodule contains the type, but shows only the lower mar- 

 gin of the head, one eye, and the thorax rolled up. The second 

 nodule contains two heads and two thorax, but in both cases the 

 heads are placed where the tails should be ; the remains are in a 

 very fragmentary condition, but they show the neck spines and 

 other characteristics of the neck ring, the eyes, the margins of the 

 l)leurte and the dorsal spines. 



Head. Marginal shape unknown. Glabella moderately con- 

 vex. Frontal lobe wider than the section across the base. Third 

 pair of glabellar furrows very deep, almost vertical to the axis, 

 neck furrow runs forwards to the axis, narrowing the bases of the 

 third pair of lobes. Eye very prominent, base on a level with the 

 end of the third glabellar furrow ; palpebral lobe ear-shaped, 

 expanded, asymmetrical. Neck furrow rounded, deep, straight 

 on the cheeks ; on nearing the axial furrow it tui-ns sharply back- 

 wards, and is continued over the hinder margin of the head as a 

 little nick and along the i-eflexed portion of the shield. The neck 

 furrow starts again on the inside of the axial furrow as a deep 

 depression overhung by the swollen third glabellar lobe, but it 

 becomes flattened out along the median line. The genal si)ines 

 have a width of over 4 millimetres at base and are over 5 mm. 

 long, measured from the inside border ; they form a flattened 

 triangle about 2 mm. deep. The axial neck spine is borne on an 

 expanded base boi'dered by the nicks in the margin where the 

 neck fui-row bends backwards ; it was shorter than the spines on 

 the thorax. The under side of the base of the axial sjjine shows 

 a raised margin. Surface covered with very fine granules, wliicJi 

 are also well shown on the outer margin above the spines. 



A considerable portion of the under surface of the head is 

 shown ; it is quite smooth and gives a depth of head on the outer 

 side of the eyes of 8 mm. The hinder margin of the neck seg- 

 ment is rounded, about 2 mm. thick, but near the genal spines it 

 becomes thicker and flatter, with the surface inclined forwards. 



Dimensions : Width between bases of genal spines r).<S cm. 



