BRITISH FOSSILS. 



Other British Species of Phacops, of the Section Dalmannia. 



1. P. sp. [fig. 16 in PL I.] 



P. Icevis, capite quam in P. cauduto, nisi lobis glabellce tumidioribus ; caudd triangulari, 

 fere aquilatera, convexa, apice acuto hand mucronato, axi 13-16 annulato, costis lateralibus 

 10-12, simplicibus, vix curvatis, ad marginem cequalem angustum abrupte terminatis. 



Length of tail l inches. There are but imperfect heads in the collections of the Geo- 

 logical Society and Geological Survey. The characters of the tail distinguish it from 

 P. caudatus; it has much more numerous ribs, which are but little curved, and not dupli- 

 cate ; the margin, too, is equal all round, not expanded or mucronate at the end. Young 

 specimens have not the full number of ribs, and a few of the upper ones are slightly 

 divided. The most prominent analogy is with P. Hausmanni, Brongn. ; but that is 

 strongly tuberculate, almost spinous, all over. P. pleuroptyx (Green), is also like, but has 

 the lateral ribs duplicate. The species of this group so closely resemble each other, that 

 we dare not give a name. Should it prove new, it might be called P. Weaveri. 



Localities. Caradoc sandstone of Long's Quarry, Damory Bridge, and Charfield 

 Green, Tortworth, Gloucestershire ; (all small) ; Woodford Green, ditto ; (large). 



2. P. obtusicaudatus. 



P. capite quam in P, caudato, sed latiore ; caudd brevi, lato, subtriangulari, apice 

 angulato, obtuso ; axi lato, convexo, 11-12 annulato, obtuso ; costis lateralibus 9, duplicatis, 

 rectis, ad marginem angustum aqualem abrupte terminatis, 



We merely note this curious species here ; it will be figured and described in Prof. 

 Sedgwick's work on Westmoreland. 



Locality. Coldwell, in flags above the Coniston limestone, Westmoreland. 



3. P. truncato-caudatus, Portlock, Geol, Rep. Tyrone, &c., pi. 2, f. 1-4, and Para- 

 doxidesl Bucepliali var., pi. 1, f. 8 (hypostome). 



P. granulatus, capite antics truncato, oculis maximis subdepressis ; pleuris obtusis, fulcra 

 ab axi valde remoto ; caudce axi IS-annulato, angusto, costis lateralibus 14-16, apice 

 emarginato. 



This interesting species, while in the large eyes and strong head spines, numerous joints 

 of the tail, and general depressed form, it is nearly allied to the other Dalmannice, yet 

 indicates moae than any other the close affinity of this section with Phacops, for the facial 

 suture is only just within the margin, the tail rather rounded than produced, the pleurae 

 have their furrows strong and curved forwards at their obtuse ends, and they are bent 

 down at the distant fulcrum, so as to be much better fitted for rolling up than is usual iu 

 Dalmannia. For the first half of the thorax they are scarcely at all bent back from the 

 fulcrum ; the posterior pleurae are more in the usual way. The hypostome is very much 

 extended at its base, is pointed, and has two pair of oblique furrows. 



Localities. Lower Silurian. Tyrone, Ireland. Coniston, Westmoreland. Horderly, 

 Shropshire. 



VAR. ft affinis. Caudce axi latiore Dalmannia affinis, Salter, in Memoirs of the Geol. 

 Survey, vol. ii., part 1, pi. 5, f. 5. 



It is to be feared there are not sufficient grounds for separating this species, founded only 

 on caudal shields. A tolerably perfect tail in Mr. D. Sharpe's collection, and an imperfect 

 one in the Survey Collection, have the axis considerably wider than in Portlock's 

 originals. Specimens, however, in Sir R. I. Murchison's cabinet, show intermediate 

 characters. 



Localities. Lower Silurian. Llandowror, Caermarthenshire. Coniston, Westmore- 

 land. 



Phacops is a widely distributed genus or group of trilobites, remarkable for the large 

 facets of the eyes, the distinct trilobation of head, thorax, and tail, the furrows separating 



