DESCRIPTION OF THE SPECIES OF PTERYGOTUS 255 
turned abruptly up, and the teeth straight, narrow, and remote, as 
in that species ; but the chela is much more slender, three inches and 
a half to four inches long, and the larger central tooth is scarcely 
longer than the diameter of the shaft itself; while the secondary 
teeth, some of them at least, approach it more nearly in size. The 
tooth at the base of the large terminal mucro is appressed against 
it, and the mucro itself (Plate XI. [Plate 22] fig. 3) is sometimes 
‘oblique. All the teeth are finely striate, the striz tending obliquely 
backward on the principal teeth. There are numerous sharp, conical, 
minute teeth between the secondaries. 
Endognaths (Maxille ?)—Most probably Plate XIII. [Plate 24] 
fig. 15, represents the first or second pair of these organs, and it is 
pretty clearly referable to P. arcuatus, and not to P. punctatus, which 
has much shorter and blunter mandibles. (Plate XI [Plate 22] fig. 6.) 
It is elongate, or even falcate, the upper lobe a greatly convex, the 
posterior portion (/) drawn out laterally instead of backwards ; the 
surface closely sculptured all over. The teeth are not oblique, 
straight, and conical as in P. punctatus, but lanceolate and curved, 
and directed outwards. About ten or eleven are free, the rest con- 
fused, either in a horny plate or mixed with sete. In this particular, 
and in the production of the lower lobe 4, it resembles P. punctatus, 
but the great curvature and elongation of the plate distinguish it. 
Base of Swimming Foot, Plate XI. [Plate 22] fig. 10. — Most 
probably, from the very convex form of the anterior edge, and the 
greatly elongate teeth, this belongs rather to the present than to 
P. punctatus. (Plate XIII. [Plate 24] fig. 14, may, perhaps, 
represent this part in the latter species.] 
Post-oral Plate, Plate XV.[Plate 26] fig. 5.—Found at Leint- 
wardine, by Mr. Alfred Marston. It differs from the corresponding 
plate in all the species, having the lobes of the apex narrow, and 
nearly their own width apart, the sinus between them being very 
wide and shallow, instead of a simple deep notch. The plate is 
cordato-lanceolate, for the upper two-thirds it is oval, the greatest 
width being rather below the upper third ; the base is rather suddenly 
contracted, and tongue-shaped. 
Thoracic (?) Appendage, Plate XIII. [Plate 24] fig. 16. — This 
has been already alluded to (p. 253), as probably belonging to the 
Species. It is more perfect than any other specimen, though only the 
impression of one side. The large ovate terminal plate @ 6, shows 
well the gradation between the ordinary plicee and the long lateral 
plaits, the middle line is bare of any ormament. At the apex are 
seen two or three of those impressed lines, which are so much more 
