210 DESCRIPTION OF THE SPECIES OF PTERYGOTUS 
Locality —UPPERMOST LUDLOW BeEps, Lesmahago, Lanarkshire, 
with several other species, and the shells Platyschisma (Trochus) 
helicites and Lingula cornea. A\\ in the Museum of Practical Geology. 
(Collected by Mr. Robert Slimon.) 
Piate I. [PLAve 12] Fics. 13-15 (AND 16, VARIETY); PLATE XV. [PLATE 26] Fic. 2 
P. PERORNAIUS. 
P. pedalis et ultra, undique squamulis minutis ornatus, capite semt-ovalt, 
thorace segmentis latts curvatis, oculls anticts minoribus granulatis. 
Synonym. A. perornatus. SALTER, in Quart. Geol. Journal, vol. xii. 
p. 31 and 28, fig. 6. 
One of the most distinct and well-marked species, and clearly 
belonging to the same section with H. dz/obus, while it is more than 
double its length and width, the largest specimen being three inches 
and a half wide and probably not less than fifteen inches in length. 
We have the head and six body segments ; the swimming feet, both 
attached and free; maxilla with palpi, the post-oral plate zz sztu, 
with some faint traces of antenne; but all these show good 
characters. 
The head (carapace!) was formerly described by me as smooth, 
but in better specimens it is closely and fully sculptured, the plice 
convex forwards. It is half a broad oval (fig. 13), three inches in 
length by three inches in breadth, and the posterior angles are acute. 
The eyes are forward and rather small, not extending over a 
space more than two-fifths the length of the head (in 7. dc/obus they 
are much more than half), and finely granulated, the lenses visible to 
the naked eye (fig. 13). 
The body segments are broader from front to back than in the 
last species, the front ones particularly, but, if fg. 16 be the same 
species, vary considerably in this respect. They are much arched 
forwards over the wide central portion, the ends are recurved as 
usual, and at less than one-third from the middle (4) a kind of fulcrum 
exists, dividing the compressed lateral area (pleura) from the more 
convex central portions. The first segment is much more rounded 
off at its hinder angles ¢ than the remainder, and the space thus left 
filled by a projecting process of the second segment (see also 
Plate IV. [Plate 15].) There is a similar but smaller process to 
1 T take leave to use-in description the term ‘ head” for convenience sake ; carapace is 
of course more correct. 
