BRITISH FOSSILS. 43 



Tig. 8, magnified at 8 a, is an entire separate ectognath. The 

 several joints of this appendage are : 



Basal Joint (coxognafhite), figs. 4 c, 8 co. The great lower lobe 

 is wide, and of a spherico-triangular shape, the inner margins as 

 well as the outer and base, being all convex. The neck is sud- 

 denly contracted and short, and the serrate terminal lobe trans- 

 verse or oblong, greatly oblique and overlapping the opposite edge 

 (not vertical as in P. acuminatus, Plate II.) Its toothed margin 

 is curved and set with thirteen small teeth. 



The other joints are attached low down, i.e. below the outer 

 margin of the basal joint, and consist of 



b. (Basignathite) short and broad-linear. 



i. (Isckygnathite) narrow triangular, produced a little at the 

 hinder angle (but not forming a lobe as in Plate VI., fig. 1.) 



m. (Merognathite) rudely trigonal, its hinder base meeting the 

 produced articular" lobe of the large penultimate joint p. 

 [Either this or the next joint ca bears the long three 

 jointed filament t. The forward salient angle of the 

 limb is formed between this and the succeeding joint.] 



ca. (Carpognathite) triangular ; its convex base outwards, its 

 apex inwards against the process of p. 



p. (PrognatJiite.^) All the preceding joints, except the great basal 

 one, do not quite equal the length of the penultimate joint p. 

 It is oblong, but narrower at the base, which is oblique, with 

 the hinder edge produced into a process (s), which reaches 

 the fourth joint (771). The outer margin is rather convex, 

 the inner a little concave, and the apex deeply and pretty 

 equally bilobed, to receive the terminal joint. 



d. (Dactylognaihite?) A regularly ovate palette, as long, measured 

 along the middle line, as the penultimate joint, and nearly 

 as broad ; it is attached to it by a prominent tubercle. 



No sculpture has been observed on the limbs. 



Metastoma or Post-oral plate, figs. 1, 10. These cordate plates 

 (referred to the posterior margin of the mouth, p. 16) occur with all 

 the species. The piece is nearly of the same narrow ovate shape in 

 this as in P. perornatus, fig. 15, but only one-third the size, 

 deeply cordate, with a sharp notch and rounded lobes in front, and 

 with the base also rounded ; the width is about half the length, 

 the lobes are covered thickly with rather large semi-circular plicae, 

 which are absent from the other parts of the plate. 



