12 CARBONIFEROUS TRILOBITES. 



to cylindrical ; marked on the sides by three sets of segmental lines, corresponding 

 to and representing the cephalo-thoracic furrows of Phacops and Caly^nene, but 

 which are not present in Proetus. The first, from the base, of these lines is 

 rounded, so as to include a circular space corresponding to the tubercle of the 

 lower cephalo-thoracic segment of Cahjmene ; the second is also slightly curved ; the 

 third nearly straight. Between the two sets of lines there is a space equal to more 

 than one-third of the whole breadth of the glabella, corresponding to the similar 

 axal or connecting space in the glabella of Phacops and Cahjmene. The cheeks, 

 slightly convex ; in form spherical triangles. Eyes, lunate ; situated on the 

 cheeks, but very near to the glabella, to the axis of which their chord or longer 

 axis is parallel ; surface under a magnifier very finely reticulated. Neck-furrow 

 deep. "Wings, or margins, separated from the front and cheeks by an imperfect 

 line or furrow which is connected with the neck-furrow, and end posteriorly in 

 sharp angles, more or less prolonged as spines. The margin is turned down, and 

 forms, on the under surface, a narrow, striated rim. 



" Thorax composed of nine segments, or, including the neck-segment, ten ; and 

 it requires some care to avoid mistaking the first pygidial for the last thoracic 

 segment as it is constructed on the same principle as those of the thorax, though 

 its parts are fused together and form one whole with the other pygidial segments. 

 The pleuripedes are compound as in Phacops, Cahjmene, Sfc. 



" Pygidium exhibiting, both in the axal and lateral lobes, distinct segments b}- 

 which it is further separated from Proetus. The axal lobe and the lateral segments 

 do not extend to the external edge, but have a considerable marginal space. It 

 may be here remarked that as this form of pygidium recurs in another Mountain 

 Limestone genus, although the corresponding forms of cephalo-thorax are strikingly 

 different, the genus cannot be satisfactorily determined from a specimen of the 

 pygidium alone." 



1. PniLLTrsTA Dekhiensis, Martin, sp., 1809. Plate I, figs. 1 — 9. 



Entomolitiius (Onircites) DEnniENSTs, Martin. Petrif. Dcrb., t. xlv, figs. 1 and 2, 



1809. 

 AsAPnus RANiCEPS, PMlUps. Geo]. Yorks., vol. ii, t. xxii, figs. 11 and 15, 1836. 

 PniixiPSiA Deumensts, Be. KonincTc. Anim. Foss., t. liii, fig. 2, 1842. 



— JoKESii, var. SEMi^'iFEKA, Portloclc. Hop. Geo], Londonderry, &c., 



p. 308, t. xi, fig. 5, 1S43. 



— Derbiensis, Morris. Cat. Brit. Foss., p. 114, 1854. 



— JoNESii, var. SEMiNiFEEA, M'Coy. Brit. Pal. Foss., p. 183, 1855. 



