54 



SILURIAN TRILOBITES. 



These are all the characters that appear to me worthy of note in this fine variety. I 

 think the large specimen figured by Murchison must belong to it ; the tubercles are 

 arranged in the same fashion. But, the front being broken off, it is not quite certain. 

 Nor do I know where to find that specimen. 



Locality. — Wenlock Limestone, Dudley ? (Murchison) ; Lower Ludlow, Ledbury 

 Tunnel (Dr. Grindrod's cabinet); Dudley Tunnel (Mr. Edgell's collection). 



Fig. 13. 



Var. y, nexilis. PI. IV. figs. 3 — 5. 



P. catjdatcs, Salter, Decade Geol. Surv., ii, pi. i, figs. 10, 11, only. 



Form broad-ovate. Length to width as eight and a half to six. Head arched, 

 obtusely pointed in front, and more than twice as wide as long. Glabella very narrow, 

 not nearly one third the width of the head. Tail broad-acuminate, not produced, its axis 

 very narrow. 



This neat variety was figured in Decade 2 of the Geol. Survey, but does not seem to 

 have been specially noticed by any author. It is not very common, except at one locality, 

 where it is in profusion. At Vinnal Hill, Ludlow, the fine mudstones of the Lower Ludlow 

 Rock are full of this trilobite. 



It is remarkable for the narrow axis to the head, a good deal resembling in this par- 

 ticular the next species, but differing entirely in the ex- 

 tremely short general form, which is rounder than even the 

 common variety, and with scarcely an angular, much less 

 a mucronate, front. The forehead-lobe is large in pro- 

 portion to the others ; the upper lateral lobe not much 

 larger than the rest; and the tail, abruptly acuminate, 

 and very broad for the species, has a very narrow axis, like 

 the next species. The side-lobes are marked by the usual 

 seven curved ribs, strongly duplicate. 



Our PI. IV, fig. 4, is the same specimen as that figured in 

 the Decade 2, pi. i, and shows the true shape of the first 

 or front ring, bearing the eyes in this subgenus. The 

 narrow riband-like band in front of the glabella is all on 

 the upper surface, not, as in the previous subgenera, mar- 

 ginal, or beneath the margin. 

 This last variety brings us very near to the characters of the P. longkaudatus, but has 

 still the abrupt, not the mucronated, front. And while the axis is very narrow, the general 

 shape is rounder, instead of longer, than the ordinary forms. 



P. caudatus, var. y, nexilis, Lower Lud- 

 low, near Ludlow. Mr. W. Edgell's 

 cabinet. 



Var. <S, aculeatus. PI. Ill, fig. 18. 

 I have before referred to this rather uncommon form (p. 52, note). 



