144' CAMBRIAN TRILOBITES. 



A most characteristic fossil, which rewarded a good day's hammering (in Mr. Hom- 

 fray's company) at the head of the marsh, Penmorfa ; and was afterwards obtained in 

 great plenty by Messrs. Homfray and Ash of Portmadoc. 



General shape a very broad oval, depressed, fully two thirds as wide as long ; t-he 

 length between four and five inches. The axis is flattened, yet distinct throughout, wide 

 and tapering from the broad iirceolate glabella to the blunt tail-axis. The head is 

 smooth and very little lobed, and the sides of the tail imperfectly radiated. 



The head is rather more than one third of the whole length, semicircular, with blunt 

 outer angles ; the glabella occupying one third the width of the head, aiid reaching to 

 the sharp marginal furrow. It is urceolate, blunt and widest in front, then a little 

 contracted, and thence widening again to the base, marked by a very distinct neck- 

 furrow. The glabella- furrows are faint, four short ones on each side, somewhat radiating 

 from the eye inwards, the lower one longest. The eye is very near the glabella, as in 

 all the genus, and placed more than half-way up the head, semilunar, and rather large. 

 The facial suture reaches the edge immediately over the eye, curves boldly out beneath 

 it, so as to leave but a third part of the posterior margin of the cheek outside it ; it is 

 marginal in front. 



The body-axis is broad, equal to the pleurae in front, but narrower than those behind, 

 and ornamented with arched striae. The pleurae are strongly facetted for rolling up, 

 convex, blunt and rounded at their ends ; the fulcrum close in toward the axis in the 

 front rings, and gradually further out till it reaches the inner fourth of the pleura in the 

 hinder ones. The pleural furrow deep, but rather short and diamond-shaped. 



The tail, a true semicircle, is somewhat flattened ; and has a short broad axis reaching 

 three fourths the w^hole length, and about half as broad as the side portions, or a little 

 more. It is marked by seven or eight distinct ribs nearly to the tip, which is promi- 

 nent and bluntly pointed. The sides are scored by five short furrows, which (faintly 

 interlined) only reach to the inner edge of the broad flattened margin, and there stop 

 abruptly. The margin is concentrically striated, of equal breadth all round. Young speci- 

 mens (fig. 6) differ but httle in proportion, but there are some specimens (one par- 

 ticularly in Mr. Ash's cabinet) which are nmch narrower than usual, and may, as that 

 gentleman suggests, be the male forms (see also figs. 6, 7). 



The labrum is long, broader at the base, but still on the whole parallel-sided. The sides 

 are not contracted, nor the front expanded, as in the iV. emarginula figured by Angelin ; 

 and the apex is an obtuse angle, at about 100°, and the tip rather acute. There is a 

 concentric furrow near the margin, and a strong pair of indentations near the tip. 



Localities. — Upper Cambrian. Lower Tremadoc Slates of Penmorfa Church and 

 Llanerch, Tremadoc ; also Castle Deudraeth, near Maentvvrog, N. Wales (Mus. Pract. 

 Geology). The figured specimens are from the cabinet of our excellent friend Mr. David 

 Homfray. 



