176 ' SILURIAN TRILOBITES. 



with the cheeks, and scarcely marked out except near the base, as in lUcBnus ; it is about 

 as broad as the cheeks. Neck-furrow quite absent. Fixed cheeks narrow, and the free 

 cheeks a small segment of a circle ; the facial suture taking its rise near the obtuse outer 

 angles, running obliquely forwards to the front margin, which it cuts rather within than 

 immediately over the eye. The eye is very forward, fully two thirds up the head, and small. 

 The body is strongly trilobed, a little shorter than the head ; the axis narrower than the 

 sides, tapering backwards slowly, and very convex. The pleurae have square ends, are 

 blunt, a good deal curved down from the fulcrum, which is at one fourth in front and 

 thence extending further and further out till it reaches one third in the hinder rings, an 

 unusual arrangement. The pleurae are flat or but slightly concave as far as the fulcrum, 

 thence sharply facetted and decurved, and striated lengthwise. The pleural groove 

 shows strongly, but only towards its lozenge-shaped outward termination. 



The semicircular, somewhat convex tail has the axis rather long, blunt, sub-cylindrical, 

 reaching three quarters down the tail ; it is smooth and has a blunt prominent tip. The 

 sides are convex, smooth, Avith no flat or hollow margin along the striate border, and no 

 furrows or ribs whatever. 



Metamorphosis ; one young specimen (fig. 17) shows only five rings. 



Locality. — Lower Tremadoc beds of Penmorfa, Tremadoc, and the neighbourhood 

 of Berth and Moel-y-gest ; e.g., Borthwood, Tyn-y-Uan, Tyddyn-llwyd farm, &c. Mr. D. 

 Homfray's fine specimens are figured, but the species is now in many other cabinets. 



PsiLOCEPHALus INELATUS, Salter. Woodcut 4L 



PsiLOCEPHALUs iKFLATUs, Salter. App., Ramsay, Geol. N. Wales; Mem. Geol. Surv., 



vol. iii, p. 316, woodcut fig. 8, 1866. 



P. prorsus frilohatus, capite inflato, et glabella conspiciie rotunda. Axis corporis 

 prominulus, caudce brevissimcE distinctissimus, et valde a lateri sejunctus. 



This small species has always appeared to me to differ from the preceding. The 



head is very convex, the glabella rounded, and sepa- 

 ^^^- ^^- rated by its convexity and by distinct furrows from the 



head. Eye? 



Body with a moderately broad convex axis, also 

 well distinguished from the somewhat convex pleurae, 

 the hinder of which are ciu-ved. I can only find 

 seven body-rings. The tail, if it belongs to the same 

 Psiiocephaius inflatus, Salter. spccics (and I bclieve it docs) is very short, and has 



Lower Tremadoc, N. Wales. ,, . , ■, i^ii • ^ i it 



,. „ u , , , . , the axis not only convex but short-conical, and marked 



Mr. D. Homfray s cabinet. •' 



out clearly all round. 

 Locality. — Lower Tremadoc, lowest beds, north-west of Penmorfa, on the Caernarvon 

 Road («, b). Upper beds, Trwyn cae lago, Portmadoc Harbour (c). Borthwood. 



