ILLJ^NUS. 



185 



Subgenus 3. — Dysplanus, Burmeister, 1843. 



Tll^nus (Dysplanus) Bowmanni, Salter. PI. XXVIII, figs. 6—13; PI. XXX, 



fig. 6, 



Ill^nus centkotus, PortlocJc. Geol. Rep., pi. x, figs. 3—6 (not fig. 9), 1843. 



II. Bowmanni, Mem. Geol. Surv., vol. ii, pt. 1, pi. viii, figs. 1—3, 1848; 



Decade 2, art. 2, p. 3, 1849; in Morris's Catalogue, 2nd ed., 

 p. 110 ; Appendix A to the Woodwardian Synopsis p. 4, 1852. 

 Siluria, 2nd ed., passim, 1859 ; also Mem. Geol. Surv., vol. iii, 

 p. 317, pi. xviii, fig. 8, 1866; and Catalogue Mus. Pract. Geol., 

 pp. 5, 19, 1865. 



II. centrotus, M'Coy. Synopsis Sil. Foss. Ireland, p. 54, 1846 ; Dysplanus, Synopsis 



Woodw. Fossils, pi. i e, fig. 19, 1852. 

 II. latus, id. Ibid., fig. 17. 



//. {D.) 3-4 unciasloiigus, convexus, lavis nisi cauda lineis nonnullis \-formibus ornatd ; 

 capife valdc convexo caudam obiusam longitudine super ante, thorace brevi. Caput semi- 

 ovatuni, convexissimum, sf/Icis axalibus brevibus, superne recurvis soepe claviformibus, per 

 tertias longitudinis capitis extensis. Gence parva declives. Oculi minimi, distantes, basi 

 capitis proximi. Anguli obtusi, nec spicula gerentes. Thoracis longitudo dimidium capitis 

 totius efficit, annulis 9; axis ejus convexus, et pleuris ante latior est; at postice, 

 in pullis pracipue, angustior. Pleurce fulcra tenus plana, dein recurva paulloque 

 decurv(B. Fulcra antice in tertias, postice in dimidium latitudinis pleurarum posita. Cauda 

 lente convexa, semiovata, obtusa: cujus longitudo \ latitudinis sua efficit; axe magno 

 superne tantum inter foveas latas conspicuo, sulcis obscuris. Latera convexa, sulco sxiperno 

 lato, et interdum {in pullo) sulcis binis obscuris. 



A large species, frequently four inches long; oblong, with blunt and very convex 

 extremities : the head not much larger than the tail, the thorax scarcely more than half 

 the length of the head, and but little more compared with the tail ; the eyes small and 

 remote ; the axis of the thorax wider than the pleurae. 



Head regularly convex, semi-oval ; glabella wider than the sides, its furrows slightly 

 converging as they reach one third up the head. Cheeks gently declining to the remote eyes, 

 which are distant from the axal furroAvs about half the width of the glabella ; and thence 

 bend steeply down to the incurved margin. The eye is very short and small, and placed 

 so far backwards as to be only its own length distant from the straight posterior margin. 

 Free cheeks very small and narrow, with blunt rounded angles (not acute and produced as in 

 //. centrotus). The facial suture is nearly direct, i. e. vertical above and below the eye. 

 The neck-furrow is distinct in casts, but beneath the cheek only ; a deep punctum at the 

 base of the axal furrows defines its position under the glabella. The section of the head 

 across the eyes is an arc of a circle about one third of the whole circumference, and from 

 24 



