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SILURIAN TRILOBITES. 



Calymene Arago, a kindred species found with C. Tristani in the French and Spanish 

 deposits, has a smooth trilobed tail, with scarcely a trace of ribs. 



Localities. — Llandeilo (or Arknig) rocks, of Gorran Haven, Cornwall, figs. 15, 16, 

 Mr. Edgell's cabinet. Budleigh Salterton, fig. 17. [Fig. 18 is added from a specimen 

 from Nehou, Normandy, where the species is very common.] 



Calymene duplicata, Murchison. PI. IX, figs. 19 — 24. 



Asaphus duplicatus, Murch. Sil. System, pi. xxv, fig. 8, 1839. 

 Calymene duplicata, Id. Siluria, 2nd edition, pi. iii, fig. 6, 1859. 



— — Salter. Mem. Geol. Survey, vol. iii, pi. xvii, figs. 15 — 20, 



1865. 



C. modica, rarissime biuncialis, alutacea, depressa, /route paullum prodactd recurvd. 

 Glabella parallela, long a ; oculi antici. Axis corporis angustus, caudce longus praangustus 

 {nee quartam partem latitudinis caudce subplance eglciens) 9 — 10-annulatus. Costa laterales 

 7 — 8, valde interlineatce, arcuatce, hand deflexa. 



An inch and a half long, — seldom more, and fourteen lines broad, 1 greatly depressed, 

 with a scarcely produced front not above one third the length of the glabella ; a very 

 narrow axis, and a many-ribbed flattened tail. The head is wide, semicircular, and 

 depressed, with a strong but very narrow margin all round. 



The glabella rather parallel-sided than parabolic (in the ? form, figs. 19, 20, somewhat 

 broader and more arched on the sides), and not occupying above one fourth the width of 

 the head. It has three well-marked lateral lobes, the lowest not greatly projecting beyond 

 the others. The glabella is depressed, and does not rise above the level of the broad 

 gently convex cheeks ; on which the small eye is placed very forward, and distant from the 

 glabella about half its width. The neck- furrow is sharp, narrow, and strong ; the axal 

 furrows narrow and deep. The surface of the head, and indeed of all the body, is finely 

 granular. 



The thorax has a very narrow convex axis, in some specimens less than a fourth the 

 whole width. The pleurae are very flat at first, and then, beyond the fulcrum, which is 

 placed far out (at one half in the front rings, and one third posteriorly) they are strongly 

 and vertically decurved, but not abruptly bent. 



The shape of the tail is semioval, depressed above, but convex around the margin. 

 The form is remarkable for the genus, being so fiat as to be more like the tail of an 

 Ogggia ox Asaphus (see fig. 21); and the numerous ribs, 9 — 10 on the axis, and 18 

 on the sides, heighten the resemblance. The axis is barely more than one fifth the width 

 of the tail in the <$ (fig. 19), and about one fourth in the ? form (fig. 24) ; — long conical, 

 and rather abruptly contracted about the middle. The end of the axis is abrupt, and 



1 Mr. J. Lee, of Cacrleon, has one specimen with the head 1^ inch hroad. 



