26 BRITISH PALiEOZOIC PHYLLOCARIDA. 



spine, in hard micaceous mudstone with Orthides. Oxford Museum D. 3. A 

 similar piece, from Church Hill, near Ludlow. In Mr. Cooking's Collection. 



G. gigas is comparable with C. Bohemica, Barrande, 1853, ' N. Jahrb.,' and 

 • Sil. Syst. Boheme,' vol. i, Suppl., p. 447, pi. 19, figs. 1—13. 



6. Ceeatiooaeis Halliana, T. B. J. and E. W., 1886. PI. II, figs. 1, 2, 3, 4 (?) ; 

 PI. IV, figs. 5, 6; PI. V, figs. 6 a, 6 b (?). 



I860. Cebatiocahis leptodacttlus, Salter. Ann. Mag. Nat. Hist., ser. 3, vol. v, 



p. 157. 

 1865. — — S.SfE. Catal. Foss., M. P. G., p. 79. 



1878. — — E..N.&E. Catal. Cambr. and Silur. Foss., 



MuB. Pract. Geol., pp. 118, 142. 



1884. — — La Touche. Handbook Geol. Shropshire, p. 



37, pi. 17, fig. 566. 



1885. — Mttechisoni (part), T. B. J. S{ H. W. Third Eeport Pateoz. 



Phyll., Brit. Assoc, pp. 337—340; 

 Geol. Mag., 1885, p. 388. 



1886. — Halliana, T. R. J. ^ H. W. Fourth Eeport, p. 230 ; Geol. 



Mag., 1886, p. 457. 



One fine large carapace (M. P. G. x \) and others smaller and less definite in 

 some respects (M. P. G. x y ; x ^ ; x ^ ; Ludlow Mus. A ; Oxford Mus. K and J), 

 and associated with segments and appendages, we regard as distinctive of a new 

 species, though formerly referred to C leptodadylus and Murchisoni, M'Coy. The 

 test, though thin, appears to have been of an unusually hard consistency. 



These carapaces in some instances have been much modified by pressure, but 

 we trace a close similarity throughout the series, allowing for probable differences 

 of age. 



The carapace (large or small) is long and smooth ; pyriform, or acutely sub- 

 ovate, deep behind, narrow in front ; gently convex on the back ; outlined by a 

 bold elliptical curve on the ventral margin, which rises up to form with the dorsal 

 edge a sharp angle in front, above the median line of the valve ; but this and other 

 features varied with age and sex, and have been modified by pressure in the 

 different specimens. The antero-ventral margin is sometimes in-drawn, making 

 the point in front more acute. The hinder margin is truncate with an elegant 

 ogee curve, full below, and ending above in the postero-dorsal angle, which is 

 often but not always sharply defined in the specimens. In some cases the ventral 

 margin is much deeper than in others. 



Five to eight segments are exposed, usually with obscure straight striaj, but 

 occasionally retaining a more complicated wrinkling at the anterior edge (PI. V, 



I 



