BRITISH FOSSILS. 6 



Affinities. But one is published which belongs to this section of the 

 genus besides our own, the Illcsnus trentonensis of Emmons (Geol. 

 New York, 2nd district), and through the kindness of Dr. Bigsby, the 

 well-known explorer of the Canadian frontier, we have seen a specimen 

 as large as our largest individuals of /. Barriensis, from Little Mani- 

 toulin Island, on Lake Huron. It differs, at a glance, from ours, in 

 the angularity of the posterior angle of the head, and its strongly 

 converging and lengthened axal furrows. Whether Dalman's Nileus 

 glomerinus, described in 1828, be this species, as Burmeister thinks it 

 may, we have no means of deciding at present. 



History. The earliest notice of the British fossil was given under 

 the name of " A new Trilobite from Dudley," by Mr. Frederic Jukes, 

 who communicated drawings and casts, and a note by Mr. J. de C. 

 Sowerby, to London's " Magazine of Natural History ;" the specimens 

 were obtained from near Barr Beacon, Staffordshire. Mr. Jukes also 

 communicated casts soon after to Silliman, for his " American Journal," 

 and it is there stated that Mr. Sowerby had referred it to a genus 

 found at Trenton Falls, the Isotelus of Dekay. Professor Green, how- 

 ever, would not admit the identity of the two genera, and denied 

 the existence of the English type in America. This was quite true at 

 the time, but it is singular enough that the Trenton limestone should 

 afford afterwards another and almost identical species. Sir R. I. Mur- 

 chison, as is well known, founded his genus Bumastus on this Wenlock 

 fossil. Milne Edwards did not adopt it, and considered it closely re- 

 lated to Nileus ; while, however, he referred the other species of Illccnus 

 to Dekay's genus Isotelus. Burmeister, in 1842, placed it in its pre- 

 sent position as a section of Illcenus ; while the species of Nileus, which 

 Dalman distinguished from all trilobites (not knowing our species) by 

 their want of trilobation, have fallen into their true position among the 

 large group of Asaphus. 



British Localities and Geological Range. SILURIAN ROCKS ; Wool- 

 hope limestone to Wenlock limestone. Wenlock formations of Hay 

 Head, near Barr, Staffordshire (Sir R. I. Murchison). Dudley, Staf- 

 fordshire. Haven, near Aymestry, Herefordshire (Rev. T. T. Lewis). 

 Woolhope limestone of Littlehope, Woolhope ; and also of Nash Scar, 

 Presteign, Herefordshire. Wenlock limestone of Ledbury, Malvern 

 (Coll. Geol. Survey.) 



Foreign Distribution. Niagara group of New York (Hall). A 

 species very like it was found near Hohcnholm, by Eichwald (Urwelt, 

 Russland, Heft, 2, 59), but it is not quoted from Norway or Sweden. 



