4 
342 REPORT—1885. 
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 
‘ 
3 
1 
from oversight. In the Lesmahago 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, &c.), in other works on Scottish Geology, in geological manuals 
&e., and in Dr. J. R. S. Hunter’s papers in the ‘Trans. Geol. Soc. Glas- 
gow, vol. vil. pp. 56, 272, &e. 
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 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 fulness 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. 0/135; and M. P. G. 
X 5!;) becomes the more prominent. The surface of the valves is deli- 
cately 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 body-segments are obliquely striated. 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 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. 
In Brit. Mus. ‘41894,’ the carapace is 60mm. long by 30mm. deep — 
(or high), and probably once rather deeper, having suffered from 
pressure. The penultimate segment is 10mm. 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.) Thue 
altogether, the animal was about 152 mm., or 6 inches, in length. 
Brit. Mus. ‘58669’ has a longer (narrowed) carapace, five body- 
rings, and a broken telson ; altogether, 61 inches long. 
In another, but smaller, individual (Brit. Mus. ‘ 41895”) the carapace, 
40 x 20 P mm. ; segments, 40 mm., but shortened ; and style, about 20 mm, 
oe 15 mm. each), make about 100 mm., or four inches, of total 
len, 
ng ten good specimens from Lesmahago we have seen two of carapace 
only; and in all the others the body-portion is shifted, and in six of them” 
