36 BRITISH PALEOZOIC PHYLLOCARIDA. 



Water, near Lesmahago, in Lanarkshire, and described (unfortunately witliout 

 good figures) by J. W. Salter in the 'Ann. and Mag. Nat. Hist. ' for March, 1860, 

 we have examined many good specimens. As mentioned by Salter, one (0. 

 papilio) has the carapace more oblong than the other (G. stygia), which is 

 deepened by a greater or less angularity on its ventral margin. In the ■woodcut 

 diagrams at p. 154 of his memoir, fig. 1 is the oblong form, and figs. 2 and 3 

 have the deep ventral angle (C. stygia), and yet they are all three termed G. 

 papilio, evidently from oversight. In the Lesmahago district multitudes of the 

 two species seem to have been embedded in the black mud (now shales) ; and 

 frequent references to these interesting deposits are made in ' Siluria,' ' Memoirs 

 of the Geological Survey of Scotland ' (especially ' Explanation of Map 23,' p. 49, 

 &c.), in other works on Scottish geology, in geological manuals, &c., and in Dr. 

 J. R. S. Hunter's papers in the ' Trans. Geol. Soc. Glasgow,' vol. vii, pp. 56, 272, &c. 



In G. papilio the carapace is sub-oblong, straight on the back, gently curved 

 below, like the prow of a boat in front, and truncate with an ogee curve behind. 

 The anterior extremity is rather sharp and is rarely preserved ; it slopes with a 

 gentle curve downwards and backwards from the antero-dorsal angle to the 

 ventral margin. The latter is somewhat convex in outline, with its greatest ful- 

 ness rather forward, but near the middle ; varying, however, with every specimen, 

 all being more or less squeezed out of their true shape. The front moiety usually 

 keeps its shape more truly than the posterior region, of which sometimes the dorsal 

 angle (as in Brit. Mus. 41896, 41897), and sometimes the boldly-curved ventral 

 portion (as in Brit. Mus. 41894, 58669 ; Cambridge Mus. 6/135 ; and M. P. G. x -Jj), 

 becomes the more prominent. The surface of the valves is delicately striate, with 

 longitudinal lines, curving parallel with the ventral margin, and coarser below than 

 near the back. In some specimens the lines are seen to converge at (or rather, as 

 it were, to start from) the postero-dorsal angles. The ventral margin is rimmed, 

 and often beset with the bases of former setjB. The body-segments are leaf- 

 marked and obliquely striated. The telson (style), relatively stout, and not much 

 longer than the laterals or stylets, is faintly ridged, and was perhaps prickly or 

 spinose. The whole adult animal was probably from four to six inches long. 



Having seen but few specimens in which the caudal appendages are well 

 preserved in their place, we get but few good measurements. 



Mr. Salter says that only three or four of the abdominal segments were free 

 (external to the carapace) ; but probably there were even five ; for in one specimen 

 (Brit. Mus. 58669 ; PI. XII, fig. 1) five segments of large size, now loose and 

 reversed, were probably exposed beyond the carapace ; and in another (Brit. Mus. 

 41895) four, with an imperfect fifth, have been shifted out of place. The 

 segments, excepting the last one, appear in their compressed condition to be half 

 as long as high, and the last one as long as three of the others. 



