90 BRITISH FOSSIL CRUSTACEA. 



the first or second pair of these organs ; and it is pretty clearly referable to P. 

 arcuatus, and not to P. (now Eurypterus) punctatus, which has much shorter and blunter 

 mandibles (pi. xi, fig. 6, op. cit.). It is elongate, or even falcate, the upper lobe 

 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. (now Eurypterus) punctatus, but lanceolate and curved, and directed outwards. 

 About ten or eleven are free, the rest confused, either in a horny plate or mixed with 

 setse. In this particular and in the production of the lower lobe it resembles P. 

 (now Eurypterus) punctatus, but the great curvature and elongation of the plate distin- 

 guish it. 



Base of Swimming-foot (pi. xi, fig. 10, Mem. Geol. Surv., Mon. I). — Most probably, from 

 the very convex form of the anterior edge, and the greatly elongate teeth, this belongs 

 rather to the present species than to P. (now Eurypterus) punctatus. 



Post-oral Plate (pi. xv, fig. 5, Mem. Geol. Surv., Mon. I). — Found at Leintwardine 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 (pi. xiii, fig. 16, Mem. Geol, 

 Surv., Mon. I). — This is more perfect than any other speci- 

 men, though only the impression of one side. The large 

 ovate terminal plate {])) shows well the gradation between the 

 ordinary plicas and the long lateral plaits ; the middle line is bare 

 of any ornament. At the apex are seen two or three of those 

 JeSstl^offZtl l £'s°k impressed lines which are so much more conspicuous on the 

 (Natural size.) opposite surface, and which seem to divide the plate into laciniae 



{a). The plate is indented at its basal end, corresponding to the central depression 

 (ridge in the cast) of the preceding joint. This joint is very irregular in shape, the 

 lobes on one side being single, on the opposed side double. Both are marked with 

 minute plicae near the edges. (See Woodcuts, page 91, Figs. 25 — 27.) 



Locality. — The above-mentioned fragments have all successively come to light during 

 the active researches of the Ludlow geologists in the quarries of Lower Ludlow Rock at 

 Leintwardine, particularly in one at Church Hill. There are many new Crustacea to be 

 described from the same quarry. 



