BRITISH FOSSILS. 



DECADE II. PLATE V. 



ASAPHUS TYEANNUS. 



[Genus ASAPHUS. BRONGNIART. (Sub-kingdom Articulata. Class Crustacea. Order 

 Eutomostraca. Family Trilobitse.) Eyes large, smooth. Facial suture marginal or 

 supramarginal in front, and ending on the posterior margin. No rostral shield. Hypostome 

 strongly bilobed. Body rings 8.] 



[Subgenus Basilicas, Salter. Facial suture marginal in front ; head but slightly lobed ; 

 pleurae furrowed transversely ; tail large, with axal and lateral furrows. 



DIAGNOSIS. A. (Basilicus) ovalis ; capite semicircitlari, angulis in 

 spinas breves productis ; cauda parabolicd, late marginatd, regulariter con- 

 vexa, apice rotundato nee acuto ; axi distincto, sublineari, angusto t mulli- 

 costato, apice abrvpto; lateribus multicostatis. 



SY.NONYMS. Asaphus Tyrannus, MURCHISON, Silurian Syst. (1837), 

 pi. xxiv. and pi. xxv., f. 1. Ogygia Tyrannus^ EMMERICH, Dissert. (1839), 

 29. Asaphus Tyrannus, MILNE EDWARDS, Crust. (1840), 3, 310. EMME- 

 RICH, Leonhard and Bronn's Neues Jahrbuch 1845 (translated in ' Scientific 

 Memoirs,' vol. iv. (1845), 273). [not of BURMEISTER, Organ. Trilob. 

 (1843), t. 5, f. 4. Ray edition (1846), 108.] 



A remarkably perfect specimen in the cabinet of W. Day, Esq., of 

 Hadlow near Uckfield, and specimens in the Geol. Survey collections 

 displaying the parts of the mouth, enable us to present a complete 

 description of this famous, but apparently local trilobite. 



Description. Length 11 inches ; breadth 6| inches. General form 

 nearly a true oval, moderately convex ; the head semicircular, the tail 

 longer and parabolic. Head smooth, with a slight concavity marking 

 off the margin, produced at the angles into short spines which reach the 

 third thoracic segment. Glabella clavate, defined in front only ; the 

 forehead lobe large, protuberant, and nearly round : beneath it, and at 

 the level of the front of the eye, is the uppermost of three obscure 

 oblique furrows. There is at the base of the glabella a tubercle, and 

 beneath it an impression marking the place of the neck furrow. Eyes 

 rather large, much arched, placed behind the middle of the head, and 

 close to the glabella ; the base of the eyelid is constricted, the lentiferous 

 surface is broad and smooth, and beneath the cornea there are very 



[II. V.] 2 E 



