188 



SILURIAN TRILOBITES. 



in most species it is nearly flat. The angles are thus truncated considerably ; and this 

 gives this rare species much the look of the ordinary //. Bowmanni, figured in the same 

 Plate, fig. 7. 



The sides are moreover radiated by 4 short furrows ; of vi^hich, as usual, the uppermost, 

 subtending the fulcrum, is broad and strong ; the second fainter, and the rest obscure. These 

 furrows do not reach above half across the sides, which are gently convex only above, and 

 then slightly decurved. Our figured specimen is a perfect internal cast in arenaceous 

 limestone, and therefore, not being broken^ conceals the fascia entirely. But a Presteign 

 specimen, in the ' Mus. P. Geology,' shows a broadish fascia with remote striae. 



The ornament of the surface is very remarkable, as above noticed. Strong, arched, or 

 rather bent strige, which run up obliquely from the sides towards the axis, inosculating as 

 they go in rather an unusual manner. They keep clear of the deflexed margin, and do 

 not cover the upper half of the sides, but reach the lower half of the short axis, and seem 

 to be continuous with its obscure arched furrows, indicating the many axal rings. Where 

 they meet from either side they take a ^-shaped form, something like the ornament ou 

 Lucina divaricata and many species of Peden. 



Localities. — May Hill Sandstone of Upper Snead, near Chirbury, Shropshire. Also 

 Presteign, Radnorshire. (Coll. by Mr. J. E. Davis : both specimens are in the Mus. Pract. 

 Geol.) 



Ill^nus (Dysplanus) Thomson:, Salter. PI. XXVIII, figs. 2—4 ; PI. XXX, 



figs. 8—10. 



Ill^nus (Dyspl.) Thomsoni, Salter. Quart. Geol. Journ., vol. vii, p. 1/1, pi. 



fig. 3, 1851. 



— — — Id. Siluria, 3rd ed., Appendix, 1867. 



— — — Id. Mem. Geol. Surv., vol. iii, p. 360, as lUcenopsis, 



in p. 231, 1866. 



//. {D.) maximus, 6 uncias loiigus, 3^ latus, I avis ; capite lente convexo, caudam semi- 

 ellipticam vix superanie, thoracem valde trilobum hac sujperante. Oculi modici, hand 

 distantes, lonyitudinem eorum a margine postico distantes. Anguli rotundati ? Genes parva. 

 Tlioracis longitudo | capitis efflcit, annulis 9 ;^ axis ejus valde convexus pleuris latior est. 

 Pleura fulcro terms {hoc postice ad dirnidium posito) plaiia, dein ahrupte declives etreflexa. 

 Cauda lente convexa, axe magno tantum inter foveas conspicuo, sulcis ormiino obsoletis. Latera 

 ahrupte lateque truncata. Fascia latissima concava, striis raris conspicuis. 



There is a close general resemblance in this bulky Llandovery species to the more 

 common //. Botomanni. I have therefore contrasted the diagnoses minutely, and beg the 



^ I think I am not mistaken in this number. We have two perfect specimens, but in both the rings 

 have somewhat slipped over each other. The relation of the species to 11. Bowmanni is so close in many 

 respects, that it can hardly be other than a Dysplanus. 



