BRITISH FOSSILS. 



DECADE II. PLATES III. AND IV. 



ILLJENUS BARBZENSIS. 



[Genus ILL.ZENUS. DALMAN. (Sub-kingdom Articulata. Class Crustacea. Order 

 Entomostraca. Family Trilobitac.) Head about a quarter of a sphere ; eyes smooth, 

 remote ; facial suture ending on the posterior margin behind the eye, marginal or sub- 

 marginal in front; hypostome entire, separated from the facial suture by a trausverse 

 rostral shield; thorax rings 9 or 10.] 



[Sub-genus Bumastus. Thorax with 10 rings, not trilobate; the axis very broad, 

 reaching to the fulcrum.] 



DIAGNOSIS. /. (Bumastus) ovali-oblongus, valde convexus, crusta crassa ; 

 capitis sulcis axalibus remotis ; oculo magno prominente, vix dimidium 

 longitudinis suce a cervice remoto, palpebra* valde convexd ; thorace arti- 

 culis 10, hand trilobato. 



SYNONYMS. " A new species of Trilobite," F. JUKES (1829), in Ann. 

 Mag. Nat. Hist., vol. ii., p. 41, figs. 8, 9, 10; "probably Isotelus" J. 

 D. C. SOWERBY, ib., p. 45; SILLIMAN, Amer. Journ. of Science (1832), 

 vol. xxiii., 1, p. 203. Bumastus Barriensis, MURCHISON (1839), Sil. Syst., 

 pi. VII. bis., fig. 3 ; ib. XIV., f. 1 ; EMMERICH (1839), Dissert. 33. Nileus ? 

 (Bumastus) Barriensis, MILNE EDWARDS (1840), Crust., vol. iii., p. 295. 

 ///. (Bumastus) Barriensis, BURMEISTER (1842), Org. Tril., 120 ; Ray 

 edition (1846), 104. Bu. Barriensis, HALL (1843), Geol. Eeport, New 

 York, No. 10, f. 4 ; No. 19, f. 2. [Nileus glomerinus, DALMAN, Arsberatt. 

 (1828), p. 136; HISINGER (1837), Leth. Suec. 16?] 



Description. Oblong-oval and very convex ; the three divisions, 

 head, thorax, and abdomen, nearly equal. Head a quarter of a sphere, 

 more pointed in front in the young specimen than in the adult, in which 

 it becomes obtuse. The surface of the head is even, and but slightly 

 marked by short converging distant axal furrows into glabella and 

 cheeks. Terminating these short furrows, and immediately above the 

 prominent upper eyelid (palpebra) is an oval space, sometimes flat of 

 depressed, and sometimes a little convex, where the crust is thickened 

 interiorly, and on which the puncta that occur so commonly on the 

 other portions of the crust are absent in some specimens, its nature 



* Dalman uses the term " lobus palpebralis" for the covering plate or eyelid : its varia- 

 tions are often characteristic. 



[ll. iii. & iv.] 2 D 



