PLATE XVI. 



UPPER SILURIAN AND DEVONIAN CRUSTACEA. 



Order — Merostomata. 



Sub- Order — Eurypterida. 



Fig. 



1. Pterygotus raniceps, H. Woodw. U. Ludlow Rock, Lesmahagow, Lanarkshire. 



(Drawn from the original specimen in the British Museum.) P. 71. 



2. Pterygotus Banksii, Salter. The carapace from the Passage Beds at the Ludlow Rail- 



way Station. (In Mr. Lightbody's Cabinet.) Pp. 72 — 74. 



3. Pterygotus Banksii, head of a very young individual. Downton Sandstone, King- 



ton. (Mr. Banks's Cabinet.) 



4. Pterygotus Banhii. The posterior segments of the body, with the telson. Passage 



Beds, Railway Station, Ludlow. (From Mr. Lightbody's Cabinet.) 



5. Pterygotus Banksii. The anterior half of the body, exhibiting the carapace, six 



thoracic segments, and the left ectognath or swimming-foot. Upper Ludlow Rock. 

 (Mr. Lightbody's Cabinet.) 



6. A metastoma or post-oral plate. Upper Ludlow Rock. (Mr. Lightbody's Cabinet.) 



7. Pterygotus ludensis, Salter. Posterior portion of body, reduced to two thirds. P. 76. 



8. Pterygotus problematicus ? A penultimate body-segment, showing the short dorsal 



ridge — not sternal, as supposed by Mr. Salter. — H. W. (Prom Mr. Lightbody's 

 Cabinet.) P. 77. 



Mr. Salter remarks : " Perhaps this represents only a variety of P. ludensis." 



9. Pterygotus ludensis, Salter. Basal joint of an ectognath, with short serrations. (Mr. 



Lightbody's Cabinet.) 



10. Parka decijnens, Fleming. Ova of Pterygotus. P. 79. 



1 1 . This specimen shows the eggs in section, as black carbonaceous spots, whereas in Fig. 



10 the external surface and rounded form of many are well preserved. 



If these eggs were enclosed, like those of the modern Limulus, in a hard and 

 horny exchorion, and deposited in the sand in the same manner, we have at once 

 a simple explanation furnished us of their abundance in certain beds. 



Figs. 10 & 11 are drawn from specimens obtained by the late Mr. Baugh, and 

 preserved in the British Museum, from the base of the Old Red Sandstone at 

 Trimpley, north of Bewdley. 



With the exception of Figs. 1, 10, and 11, these are all re-drawn from Mr. 

 C. R. Bone's excellent figures in plates xii and xiv of Messrs. Huxley and Salter's 

 Monograph on the Eurypteridae. ('Mem. Geol. Surv./ Mon. I, 1859.) 



