UPPER SILURIAN ROCKS OF THE PENTLAND HILLS. 161 



The telson tapers regularly to a sharp point. The posterior portion of it is angular, 

 with a sharp median ridge, but anteriorly this ridge expands into a flat triangular area. 



The proportion of this specimen to the one described above is roughly as 1 to 3, 

 which would make the telson of the latter some 51 mm. in length and 9 mm. in breadth. 



If these posterior segments belong to Drepanopterus, they present a very close 

 resemblance to those of some Eurypterids. The shape of the limb, however, and the 

 proportions of the carapace, seem to me sufficiently distinctive to justify the formation 

 of a fresh genus for the reception of this form. This genus would, as Mr Peach first 

 suggested to me, occupy a position between Eurypterus and Stylonurus. The form it 

 most nearly approaches in the shape of the appendage is that described by Hall * as a 

 sub-genus of Eurypterus, under the name of Dolichopterus. Some specimens in Mr 

 Hardy's collection will, I think, throw further light on the structure of this form. 



DESCRIPTION OF FIGURES. 



Plate I. 



Fig. 1. Portions of the carapace and anterior body segments of Stylonurus omatus. x £. 



Fig. 2. Posterior segments of the same species, x £.. 



Fig. 3. Portions of the ventral surface of the carapace, natural size, to show the sculpture. 



Fig. 4. Portion of the sculpture on the ventral surface, probably of the abdominal appendages, nat. size. 



Fig. 5. Outline of central lobe of genital plate, nat. size. 



Fig. 6. One of the elongated limbs, nat. size. 



Fig. 6a. Two joints of the same limb from the other half of the slab, to show the crenulated margin. 



Fig. 7. Outline of the metastoma and ectognath. nat. size. 



Fig. 8. Detached telson probably belonging to this species. x i. 



Plate II. 



Fig. 9. Cast of the most perfect specimen of Stylonurus macrophthalmus. n. sp., nat. size. 



Fig. 10. Carapace of the same specimen from the other half of the slab. nat. size. 



Fig. 11. Telson of St. macrophthalmus. nat. size. 



Fig. 12. Eurypterus conicus. nat. size. 



Fig. 13. Outline of metastoma of E. conicus. 



Plate III. 

 Fig. 14. Eurypterus conicus. nat. size. 

 Fig. 15. E. cyclophthalmus. nat. size. 



Fig. 16. Drepanopterus pentlandicus, carapace and greater part of body, with one limb. nat. size. 

 Fig. 17. Posterior segments and telson of a smaller specimen of D. pentlandicus. nat. size. 



* Paleontology of Nevj York, vol. iii. p. 414. 



