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SILURIAN TRILOBITES. 



Locality. — Caiiadoc Rocks of North Wales and Shropshire ; Cader Dinmael, near 

 (Jorwen, Denbighshire (fig. 14); of Nantyr, near Llanannon, Denbighshire (fig. 12) : Capel 

 Gannon, same county (Woodw. Mus.) : Cressage, Shropshire ; fig. 13 (Mus. Pract. Geol.). 



IIomalonotus Brongniarti, DeslongscL PL X, figs. 15 — 17 ; PI. XIII, fig. 9. 



Asaphus Brongniarti, Deslongschamps. Trans. Soc. Linn. Calvados, vol. ii, p. 301, 



pi. xix, xx, (fig. 12?) 1825. 

 Homalonotus Brongniarti, Marie Rouault. Bull, de la Soc. Geol. France, 2 me Ser. 



vol. vi, p. 379, 1849. Id. in vol. viii, p. 370 (not of 

 De Verneuil, id., vol. xii, pi. xxiii, fig. 1). 

 — — Salter. Quart. Geol. Journ., vol. xx, p. 290, pi. xv, 



fig. 1, 1864. 



P. 9-uncialis et ultra, oblongo-ovatus, capite cauddque minoribus. Glabella parabolica, 

 vix lobata, sulco distincto circumdata, d fronte curvd bene sejuncta. Gena elevates, oculi 

 retrorsi. Thorax trilobus, axe lato. Cauda rhomboidea, ut longa quam lata, axe distincto 

 8 — 9-annidato ; lateribus subplanis Icevibus, sulcis angustis 7 — 8 ; margine serrato. 



Although the figures in the Calvados Transactions are rather out of date, yet the care 

 which M. Deslongschamps took to figure all the varieties leaves no doubt as to what 

 species he intended. It was rather a large fossil ; some of the foreign specimens appear 

 to have grown more than nine inches long, and it is rather conspicuous for the trilobation 

 of the body. Deslongschamps has not shown the curious serration of the tail-margin, 

 but except in that point his figure is exact. The swelled front border, the slightly lobed 

 parabolic glabella, the backward eye; and the tail, with its shortened axis and almost 

 smooth sides, — are very well figured • and his description is characteristic and complete. 



I will only describe our own specimens, and add a note upon the body-rings from the 

 Prench author, who had larger specimens than we possess. 



Head an inch long, of which the parabolic glabella occupies seven lines, and is eight 

 lines broad at the base, depressed, very slightly lobed, and well distinguished from the 

 sides by a shallow furrow. The front margin (" chaperon") is much elevated, and the 

 interval between it and the cheeks depressed. The latter are tumid and rather narrow ; 

 the small eyes placed considerably behind the middle : the free cheek triangular and 

 smooth, except on the vertical outer margin, which is roughly granular all over. 



The body in Prench specimens is very convex, but not semicylindrical, being depressed 

 above. The sides bend down abruptly. The central lobe is well marked out, and is 

 wider than the pleurae in front, but narrower behind ; the distinct trilobation takes place 

 some distance within the fulcral points. The facet is large and distinct, and the pleural 

 groove nearly reaches the broad tip. The separate figures of the pleurae given by Des- 

 longschamps much resemble our figure 16, ad. 



