174 BRITISH PALAZOZOIC FOSSILS. [Crustacea 
one largest and curved downwards; neck-fwrrow terminating in a large oblique tubercle at each end; eye- 
line nearly vertical, cutting the anterior and posterior margins in a line with the eyes, which are lunate and 
smooth; thoraz of ten joints, pleurze with distinct facets and obtuse ends, pleural furrow slightly oblique ; 
pygidium semielliptical, with a smooth margin, both the axis and side lobes with distinct segmental furrows, 
the latter duplicate at their ends. 
This genus differs from Proetus in the lateral angles of the buckler being produced into long spines, 
in the lateral segmental furrows to the glabella, the large oblique tubercles terminating the neck-furrow, 
and the distinct segmental furrows of the lateral lobes of the pygidium. 
Subsequently to the publication of this genus under the above name, in my Synopsis of the Silurian 
Fossils of Ireland, Burmeister, in the second edition of his work on Trilobites, p. 100, characterised it similarly, 
and pointed out particularly its distinctions from Proetus. 
ForBESIA LATIFRONS (J/‘Coy). 
Ref —MCoy, Sil. Foss. Irel. t. 4. f. 11. Mem. Geol. Sury. Vol. II. Pt. 1. t. 6. fig. 1. 
Sp. Ch.—Ovate; head and thorax of equal length; pygidium as long as six segments of the thorax ; 
cephalic shield nearly semicircular; spinose angles reaching to the sixth thoracic segment; glabella wider 
at base than in front, not reaching the anterior margin; /Jimb thick, tumid; articular margin and neck- 
segment also thickened, the extremities of the latter forming very large tubercles; eye-lines cutting the 
anterior and posterior margins nearly in a line with the outer edge of the eye, inclining outwards and 
forwards from the eye-lobe in front, running parallel to the axis behind, till it reaches the articular 
margin, which it cuts obliquely outwards nearly in the middle; eyes large, very close to the glabella; axis 
of body about as wide as the pleuree, the segments strongly tubercular at the ends; pygidium semicircular, 
nearly twice as wide as long, with a broad smooth margin; azis conical, not reaching the margin of 
seven narrow ridges; side lobes with fine broad, obscurely-defined ribs, each with a faint duplicating furrow. 
Length ten lines; length of head four lines, width of head seven lines, 
Position and Locality—Very abundant in the Upper Ludlow rock of Underbarrow, Kendal. 
Forpesia Stoxesti (AZurch. Sp.) 
Ref. and Syn—Asaphus Stokesii Murch. Sil. Syst. t. 14. f. 6. 
Sp. Ch.—Ovate; head semielliptical, the angles reaching as far as the pygidium, length of the middle 
portion equal to half the width; ¢horaz as long as the head, axis only as wide as the pleure in front, 
and considerably less wide behind, knee at about one-third the width from the axis (a little more in front, 
a little less behind), ends of the axal segments not distinctly tubercular; pygidiwm semielliptical, with a 
broad tumid margin and six wider flattened ribs on each side, each divided by a fine mesial impressed 
line. Length five and half lines, width of head three and half lines. 
This species differs from the F’. Jatifrons (M*Coy), by the much greater size of the lateral cephalic 
angles, by the longer and narrower head, the narrower axis, and want of the distinct tubercles to the ends of the 
axal segments. 
Position and Locality—Wenlock limestone of Ledbury, Herefordshire. 
2nd Tribe. POZCILOPODA. 
In this tribe the feet are constructed on two different types, the thoracic ones (six pairs) being strong, 
cerustaceous, didactyle, and ambulatory; but the abdominal ones forming transverse, membraneous leaflets 
subservient to respiration. In the recent type, the mouth is without jaws, but the bases of the feet which 
