240 DESCRIPTION OF THE SPECIES OF PTERYGOTUS 
globular shape, not crowded over each other, but arranged in nearly 
one plane so as to form a disk. 
A long pedicle, fully a line broad, is attached near the centre of 
the disk so formed, or sometimes nearer its margin; and from the 
point of attachment the surface of the general enclosing membrane 
is radiated or plaited to the margin, but only on one side of the disk. 
The plaits are depressed lines, dichotomising and inosculating a little, 
but seem to have no reference whatever to the arrangement of the 
ova, which they cross without being interfered with by them. 
The appearances presented would be best explained by the 
supposition of the fossils having been membranous disks of only 
a moderate thickness, and containing a single series of ova in the 
thickness of the disk. They are not superimposed one on the other, 
as they would have been had they been contained in a pyriform sac,. 
but set at equal short distances apart, as if kept in their places by the 
membrane of the disk that enveloped them. 
Localities-—-LOWER OLD RED SANDSTONE, Balruddery, Perth- 
shire; and Leysmill near Arbroath, Reswallie, Tealing, Carmylie, 
and other places in Forfarshire. The specimens are chiefly in the 
collections of Lord Kinnaird, Mr. Powrie, and of the Watt Institution, 
Dundee. One or two are in the Museum of Pract. Geology. 
PLATE XIV. [PLATE 25] Fics. 1 To 13; PLATE IX. [PLATE 20] Fic. 18?; 
PLATE XII. [PLATE 23] Fics. 1 To 5 (AND 6?). 
P. LuDENSIS. 
P. major, segmentis corporis omnibus transversts, decimo bis quam longo 
latiore, penultimo subquadrato vix expanso, supra caring percurrentt , caudé 
ovalt breviapiculata obtusicarinata. superficie toto plicts curvatts simplictbus 
ornato. 
Under this name I would now describe, with but little doubt of 
its specific distinction, the fragments of a fine species very abundant 
indeed in the transition beds of Ludlow, shown as they are in the 
railway cutting near that town. All the specimens are in the 
cabinets of Mr. Lightbody and his son. The same species is found 
at Trimpley near Kidderminster, and we are indebted to Mr. G. E. 
Roberts for the means of illustrating some points not clear in the 
specimens at Ludlow. 
The materials consist of several body rings of large size, Plate 
NIV. [Plate 25] figs. 2, 3, 4,11; a fragment of the caudal joint, 
