74 BRITISH FOSSIL CRUSTACEA. 



The Antenna (Geol. Surv. Mem., Mon. I, pi. xii, figs. 30 and 40) are remarkably 

 slender and straight ; the base is large and broad, suddenly attenuated into the shaft, 

 which is only a tenth of an inch wide, and three quarters of an inch long, beset with close 

 small teeth, and furnished with three larger conical ones nearly straight ; the central one 

 as long as the width of the shaft. In the fragment of an antenna figured by Mr. Salter 

 (Mon. I, pi. xii, fig. 40) from the Ludlow Rocks, the intermediate teeth are a little 

 longer in proportion. 



Ectognaths. — The basal joints are flask-shaped, much more elongate in the neck than 

 those of P. bilobus, and less swelled at the base. [It is possible, Mr. Salter adds, they 

 may not belong to this species at all, but to Eurypterus linearis, a species which occurs in 

 the same beds ; we do not yet know this joint in Eurypterus. 1 ] The base is subquad- 

 rate, quite rectangular on the outer upper margin ; the notch for attachment of the other 

 joints is immediately beneath this angle, and tapering into the long neck, which has a 

 sharp ridge posteriorly, and, together with the terminal lobes, equals the length of the 

 basal portion. The teeth are minute. 



The Swimming -foot (PI. XVI, fig. 5) has a characteristic shape ; the upper joints 

 (fourth and fifth) are rather narrow ; and the penultimate (p), instead of being simply 

 conical, as in Pt. bilobus, is ovate, with the outer border especially convex. It is notched 

 above to receive the fifth joint, and below divided into very unequal lobes. The terminal 

 palette (d) is true oval, rather blunt at its origin, and more pointed at the extremity. It 

 is nearly equal to the penultimate joint in length, but considerably narrower. 



The Post-oral plate (PI. XVI, fig. 6) differs a little in shape, but not specifically, unless 

 the greater amount of ornament in some specimens be considered sufficient to separate it. 

 The shape is elongate oval, the greatest width is at the upper third, the base is subtruncate, 

 the apex has a shallow obtuse notch. At the lower fourth there is evidently a tubercle 

 of attachment, and such as occurs in a more linear shape in other species. [It is desirable 

 to find out the post-oral plate of Eurypterus, which is probably very similar.] 



The sculpture is very conspicuous over the upper half; it consists of nearly straight 

 or very slightly curved plicse arranged in arched lines, and ending abruptly against the 

 outer margin. In the sandstone specimens the sculpture does not extend so far down, 

 but it is identical in structure. 



Localities. — Upper Ludlow Rock, Ludlow Lane, Whitcliffe (and Batchcot?), Parian, 

 exterior slope of the Woolhope Valley (Mus. P. G.), Kington, Herefordshire (Mr. R. 

 Banks' cabinet), Passage Beds, Ludlow Railway cuttings (cabinets of Messrs. Lightbody 

 and Marston, Ludlow Museum, British Museum, and Museum of Practical Geology, 

 Jenny n Street.) 



is distinct, but it is uncertain if this specimen be of the same species ; it has a strong median groove down 

 the under side, and is less expanded in form than P. Banksii. 



1 Several of these minute detached basal joints are figured by Mr. Salter (see Mem. Geol. Surv., 

 Mon. I, pi. xii, figs. 29 and 29a), but as they present no character of importance, and as their connection 

 with Pt. Banksii seems doubtful, we have not thought it needful to reproduce them here. — H.W. 



