156 BRITISH PALAZOZOIC FOSSILS. [CrusTacea. 
appendage; the pygidiwm terminates in six broad, ovate, leaf-like, semimembranous flaps. Length of 
thorax and pygidium two inches two lines, width two inches three lines, width of axal lobe six lines. 
This magnificent trilobite can only be confounded with the Kccoptochile clavigera (Bey. Sp.), from 
which it is distinguished by the much greater width of the lateral lobes of the thorax, and the thin, 
flat, Jeaf-like appendages of the pygidium, which in that species resemble thick pear-shaped clubs. A 
comparison with the old description and casts, published by Green, induces me to place this trilobite in 
his little-known genus Cryphewus, and to doubt very much the propriety of separating the genus Hecoptochile 
of Hawle and Corda from it; but as there are two forms confounded under this name by Green, and the 
one now best known in America by his name being the type allied to Phacops arachnoides (Asteropyge 
H. and C.), I use the Bohemian genus for the present fossil, in accordance with the suggestion of M. de 
Verneuil. 
Position and Locality.—The nearly entire specimen described was collected by Prof. Sedgwick from the 
black shale, two miles N. of Builth, Radnorshire. 
Explanation of Figure.—P1. 1. F. fig. 14. Entire specimen, natural size. 
Genus. ZETHUS (Pand.) (as defined by Volborth). 
Syn. = Cybele Lovén. + Atractopyge Hawle and Corda. 
Gen. Ch.—Ovate, rapidly tapering from the cephalic shield which is nearly semicircular, with the lateral 
angles forming short spines; glabella clavate, narrowing towards the axis, coarsely tuberculated, three small 
straight more or less distinct segmental furrows on each side of the base; neck-segment strong and smooth ; 
cheeks triangular, flattened, coarsely tuberculated, posterior margin thick and smooth; eyes forming small 
tubercles near the middle of the anterior margin, with an apparently smooth cornea; facial suture termi- 
nating at the angles of the head behind; thoracic segments eleven* ; pleurw divided by a small angulated 
furrow, their extremities often produced; pygidium triangular, axis rounded with many joints, much curved 
downwards; side lobes nearly vertical, the ribs few (four to seven) deflected nearly from their origin. 
This genus is intermediate between Phacops and Calymene in the form of its head and glabella, and 
agrees with the former in the number of body-segments, and with the latter in the course of the eye-line ; 
the pygidium approaches in some measure to Hncrinurus, which differs by its elevated eye-pedicles, and 
the Phacops-like course of the eye-line. 
I follow Dr Volborth (see his paper Ueber einige russischen Trilobiten in the Verhandlungen der 
russisch-kaiserlichen Min. Gesellschaft zw St Petersburg for 1847) in referring Cybele of Lovén to Zethus 
of Pander; and after a most careful consideration of the different species, I find so imperceptible a gradation 
in structure of pygidium from <Afractopyge, in which the four upper axal segments are prolonged into the 
side lobes, and deflected close along the axis (believing with Lovén that those are really pygidial segments), 
to those in which two or three more lateral ribs are added, that I also feel satisfied that Atractopyge of 
Hawle and Corda should be added to Zethus. 
ZETHUS ATRACTOPYGE (M°Coy). Pl. 1. G. fig. 1 to 5. 
Syn.— Cybele verrucosa Lovén, (not Zethus verrucosus Pander) = Atractopyge verrucosa (Hawle and Corda). 
Sp. Ch.—Cephalic shield coarsely tuberculated, rounded, about three times wider than long; glabella 
clavate, convex, front obtusely rounded, not reaching the margin, basal two-thirds narrowed, nearly parallel- 
sided, with three strong nearly equal segmental furrows on each side, eyes small, about one-third nearer 
the glabella than the lateral angles; neck-segment narrow; thoraz having the segments narrow, those of 
the axis terminating in a tubercle at each end (not well shewn in the figure) ; plewrw having a horizontal 
* The difficulty, without great care, of distinguishing between the thoracic and pygidial segments may account for the 
different numbers occasionally assigned to the former. 
