ILL^NUS. 



187 



Pembrokeshire. In Ireland : — Tyrone ; Portrane, Dublin ; Chair of Kildare ; Wexford ; 

 &c. Llandovery Rocks, Girvan, Ayrshire, abundant; Builth; Llandovery; Haver- 

 ford vs^est (with Thomsoni), and other localities in S. Wales. Kilbride, Co. Galway 

 (Sir R. Griffith). May Hill Sandstone, Shropshire, rarely, viz. — Norbury, PI. XXVIII, 

 f. 6 ; Chirbury. Also in the Purple (' Tarannon') shales of the Onny River, Shropshire 

 (Cabinet of the late H. Wyatt-Edgell, Esq.), Our figures are chiefly from the Museum 

 Pract. Geology. The species never occurs in Wenlock rocks, and but rarely so high as 

 May Hill Sandstone. 



Mr. Wyatt-Edgell's cabinet contains a caudal shield, clearly intermediate in form between 

 //. Bowmanni and our next species, which must be regarded therefore as a subspecies 

 only. We shall term it //. csmulus : — 



Subspecies J. 



Ill^nus (Dysplanus) ^mulus, n. sp. PI'. XXVIlI, fig. 5. 



//. (D.) modicus, forsan triuncis, depressus, superficie imbricatd, caiidd {ccefera non 

 adhuc inventa sunt) lata. Lovg. cauda 1 6 lin., lat. 2 unc. Cauda semicirculata, ante 

 subrecta {angulis iruncatis exceptis), postice cequabiliter rotundata. Axis dimidiuni cauda 

 vix efficiens, brevis ; sulcis axalibus latis convergentibus, ad marginem superior em profundis 

 latisque. Annuli in axe antico .5-6, inconspicui, arcuati. Latera sulcis 3-4 brevibus et 

 radiantibus distincta, quorum supermini latus profundius. Fulcra ab axe dimidium latitudinis 

 ejus distantia. Anguli truncati, facie externa curvd. Margovalde deflexus. Fascia lata. 



A single caudal shield or tvro only of this remarkably fine fossil have yet occurred. They 

 are from that as yet little known formation, the May Hill Sandstone, and are in the 

 collection of Silurian fossils in Jermyn Street. Collectors should search for the head and 

 body-rings, which probably would indicate a short obtuse species, depressed above, but con- 

 vex on the borders. It can only at present be regarded as a subspecies of the preceding. 



Tail 2 inches wide, and 1 inch 4 lines long ; semicircular, convex on the steep sides 

 and depressed above. The anterior border is rathel* straight. The axis is broad above, 

 defined there by wide axal depressions, and not quite equal in width to half that of 

 the front margin ; from thence greatly converging shallow axal furrows reach one third 

 down the tail. The axis is, however, really extended further, and is faintly indicated 

 as far as nearly half-down the tail ; it forms nearly an equilateral triangle — our figure 

 does not show this quite correctly. Faint arched rings, five or six in number, ornament 

 the upper part, and seem to run almost continuously into the strong squamate ^-shaped 

 plicae which ornament the surface. These are stronger, sharper, and more remote than 

 in any species with which I am familiar. 



The sides show a remote fulcrum, placed at about half the width of the axis 

 away from it, and thence a suddenly recurved facet, which is convex outwards, while 



