Notes on Species of Ceratiocaris. 393 



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 

 there termed C. papilio, evidently from oversight. In the Lesma- 

 hago district multitudes of the two species seem to have been 

 imbedded 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, etc.), in other works on Scottish Geology, in geological 

 manuals, etc., and in Dr. J. S. Hunter's papers in the Trans. Geol. 

 Soc. Glasgow, vol. vii. pp. 56, 272, etc. 



Carapace 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 pre- 

 served ; 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 fullness near the 

 middle and rather forward, but varying 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 -^,-) becomes 

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

 with longitudinal lines, curving parallel with the ventral margin, 

 and coarser on the ventral than on the dorsal region. In some 

 specimens the lines are seen to converge at, or rather, as it were, to 

 start from, the postero-dorsal angles. The telson (style), relatively 

 stout, and very little longer than the laterals or stylets, was faintly 

 ridged, and 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 (as in Brit. Mus. 41894), we get 

 only 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) 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. The segments, excepting the last one, 

 appear in their squeezed condition to be half as long as high, and the 

 last one as long as three of the others. 



In Brit. Mus. 41894, the carapace is 60 mm. long by 30 mm. 

 deep (or high), and probably once rather deeper, having suffered 

 from pressure. The penultimate segment is 10 mm. long, and if 

 there were four of that length (40 mm.), with the ultimate segment, 

 the body-rings would be nearly 80 mm. The telson was 25 mm. 

 (stylets 18 mm.). Thus, altogether, the animal was about 152 mm., 

 or 6 inches, in length. 



Brit. Mus. 68669 has a longer (narrowed) carapace, five body- 

 rings, and a broken telson ; altogether, 6^ inches long. 



