ILLyENUS. 



183 



7. Illcpnopsis, Salter, 1865. Eyes remote, forward; glabella-furrows reaching the 

 front ; head not gibbous, only convex ; pleurae grooved. [Probably a distinct genus.] 

 Lowest Silurian, British. 



II. {Illcenopsis) T/iomsoni, Salter. [Not Illcenus Thomsoni.'] 



§ 2. — Body scarcely trilobed : labrum short. 



8. Bumastus, Murchison, 1837. Eyes large, remote, backward; ten body- 

 Lower and Middle Silurian, but chiefly Upper ; universal. 



rmffs. 



II. Barriensis, March. II. insignis. Hall, 



//. carinatus, Salter. II. Trentonensis, Hall. 



Fig. 46. 



yenus 1. — Of Octill^nus we have no British types. It 

 is a Lower Silurian Bohemian form. We give a woodcut (fig. 46), 

 as it is so peculiar a form of the group, from Barrande's figure. The 

 enlargement of the first pair of pleura3 is a very unusual character 

 in the Asaphoid or smooth Trilobites. 



Subgenus 2.— Panderia, Volborth, 1863. 

 Ill^nus (Panderia) Lewisii, n. sp. PI. XXVI, figs, 2, 2«, h (nat. size and magnified. 



11. {Pand.) minimus [forsan junior?), uncia longus, vix ^ latus, ovatus, capite 

 {glabella pracipue) gibbo, thoracem longe super-ante, et caudd planatd bis fere longiori. Caput 

 subtrigonum, f route paulloproducta, angulis obtusis marginatis. Glabella post verticeni gibha, 

 I latitudinis capitis efficiens, oculos attingens. Sulci axales brevissimi, ad basin glabellcs 

 solum conspicui. Oculi magni, glabellam appressi, dimidium diametri suonm a margine 

 distantes. Thorax axe medico, antice latiori, pleuras subplanas superante. Cauda brevis 

 semiovata planata, axe long o, per totam longitudinenv conspicuo . 



Had not Dr. Volborth figured two species of this very distinct subgenus, one of which 

 is given on the next page, I should have taken this for ihegoung of some undescribed species. 

 The large size of the head and eyes relatively to that of the tail, and the more complete 

 marking out of the axis in the caudal shield, are characters belonging usually to young 

 specimens. But there can be little doubt we have here nearly, if not quite, the adult 

 forai of a subgenus not heretofore described from Britain, and apparently rare even in 

 Northern Europe. We owe our single specimen to the care of Mr. Lightbody, who 

 obtained it for this work from the cabinet of the Rev. D. P. Lewis, of Guilsfield, near 

 Welchpool. It is a valuable addition to British fossils. 



The width of our single rolled-up specimen at the base of the head is 5 lines, 

 and, the length of the large head being fully 4 lines, we may reckon the whole specimen 

 as 7 or 8 lines long. The form, unrolled, would be ovate, the gibbous head being 



