ILLiENUS. 



201 



half their own length from the hinder margin, while in the kindred species they are 

 only their own length in front thereof. 



Thorax deeply trilobate ; the arched rings broad, and flat from front to back ; the 

 pleurae are equal to the axis in width, and are arched forwards instead of at all back- 

 wards ; their fulcrum is extremely close to the axal line, seemingly about one fourth out, 

 and from thence the pleiu'se are covered by longitudinal lines, not very close-set ; their 

 ends are truncate. 



The tail (in the figured specimen from the Woodwardian Museum) is compressed ; but it 

 was evidently convex ; with a narrow axis, defined by broad and rather deep axal furrows, 

 which extend, however, but a short distance, and do not much converge. The axis 

 shows four annulations within the crust (our figure has too many). The sides slope 

 evenly down to the thickened margin, which is not at all flattened or recurved ; and the 

 internal fascia is concave, broad, and coarsely and remotely striated with imbricate 

 sculptured lines. 



I have described the original specimen, but believe the caudal shield fig. 5, which 

 does not show the axis ribbed, to be the same, and to show the true form of the tail. 



LQcality. — Coniston ; Sunny Brow ; and Horton in Ribblesdale, Westmoreland. In 

 Caradoc or Bala limestone (figs. 2, 4, Woodw. Mus.) ; fig. 5, Mr. Wyatt-EdgelPs 

 Cabinet. 



Ill^nus (III.) Murchisoni, Salter. Pi. XXVI, fig. 1, and PI. XXX, fig. 7. 



Ill^nus Rosenbekgii, Salter. Mem. Geol. Surv., vol. ii, pt. 1, pi. v, figs. 6 — 8, 

 1848. Not of Eichwald. 



— Murchisoni, Id. Sedgwick's Synop. Woodw. Mus., Fasc. 1, Appendix, 



p. iv, 1852; description only. (Only exclude figures of 

 Westmoreland specimens, pi. ic, figs. 33 — 35, which are 

 II. Rosenbergii.) See p. 199. 



— — Id. Decades Geol. Survey, No. 2, Art. ii, p. 4, 1849. 



77. {lllanus) mac/mis, 6-7 uncias longus, ellipsoideus, obtusus, convexissimus, capite 

 ei thorace ejusdem longitudinis., caudd vix minori. Caput pars quarta splmrce est, 

 sulcis axalibus brevibus, rectis, hand ultra oculos tractis. Oculi majores, vicini, a 

 margine postico diametrum siium distantes. Anguli capitis quadrati. Thorax longus, axe 

 latissimo pleuris subrectis longe latiori, ad fulcrum proximo. Cauda convexa semicircu- 

 lata, angulis haud truncatis, margine obtuso ; axe obscuro lato, fascia angustd. 



More desirous to identify the closely related forms of this genus than to multiply 

 species, I too hastily (in 1852) united the fossil from Llandeilo that is figured in the 

 ' Survey Memoirs ' with one which is common in beds of the same age in Westmoreland. 

 The latter will be found in p. 199, and I believe it to be the true //. Bosenbergii of 

 Eichwald. The Llandeilo species, however, is clearly distinct, as pointed out by myself 

 in the Appendix to Prof. M'Coy's ' Woodwardian Catalogue and, as there are two 

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