DESCRIPTION OF THE SPECIES OF PTERYGOTUS 219 
Prats I]. [PLATE 13]; ALSO PLATE NIII. [PLATE 24] Fics. 1-4; 
PLATE NV. [PLATE 26] Fic. 1, 
SECTION 2. 
PTERYGOTUS ACUMINATUS. 
P. magnus, 3-pedalis, elongatissimus, capite oblongo angulis quadratis, oculis 
rotundis minoribus: segmentis corporis 12, guorum quingue anticis transversis 
bicarinatis, religuis subguadratis, penultimo oblongo: cauda ovata in apiculum 
longum producté. 
-SYNONYMS. =P. acumtnatus, SALTER, Quart. Geol. Journal, 1855, vol. xii. 
p- 29, fig. 4. Po maximus, id. p. 28, fig. 3. Slémonia (1856), D. Pace, 
Advanced Text-Book, p. 135, fig. 3. 
That the two figures above referred to belong to one and the 
same species is, I think, almost certain, and all the fragments in our 
Plate II. [Plate 13], &c., occur in juxtaposition, and are doubtless 
remains of the same large Prerygofus, the finest of the four or five 
species which were collected from Lesmahago by Mr. R. Slimon. 
Although not so gigantic as those next to be described, P. acuminatus 
is yet a very large species, and more elongated in all its parts than 
any of the others. The head is nearly five inches broad and six and 
a half long, and the seven hinder or abdominal rings, which are 
different in shape from the anterior thoracic ones, are almost square 
instead of transverse ; while the tail is ovate anteriorly, and behind 
is drawn out into an apiculus equalling the anterior portion in length. 
The Head, Plate II. [Plate 13] fig. 1, is oblong, with straight 
sides, except at about the anterior third, where it is contracted so as 
to give it a suburceolate shape; the front is somewhat rounded, and 
as well as the sides crenated, or rather tuberculated along the edge ; 
the eyes are placed at the anterior angles, as forward as in P. anglicus,. 
but much smaller in proportion, oval, about six-tenths of an inch 
long, and very prominent. 
Of the body rings, which are twelve in number, including the 
tail joint (telson), we have several good specimens. Of these the 
chief are figs. 10 and 11 in Plate II. [Plate 13]. The former is 
of the natural size, a young specimen, showing the whole of the body 
rings ; the two hinder ones are left out for want of room in the plate, 
but these are well seen in fig. 11. The rings are arched, and were 
probably very convex, and both the front and back edges of the 
