STYLONURUS LOGANI. 129 



indicate two or three species of females, while the several forms in Plerygotus bilobus 

 would probably indicate the males with their chelate antennae. But to establish this 

 position, most palaeontologists would require evidence as conclusive as that obtained by 

 Mr. Binney in the case of Stigmaria and Sigillaria} 



Formation and Locality. — Old Red Sandstone, Forfar. 



Species 6.— STYLONURUS LOGANI :— H. Woodward. PI. XXIV, fig. 1. 



Stylonurus, Page. Brit. Assoc. Rep. Glasgow, 1855, p. 89. 



— spinipes, Page. Advanced Text-Book, 2nd edition, 1859, p. 181, fig. 1 



(no description). 



— Logani, H. Woodward. Geo]. Mag., 1864, vol. i, p. 197, pi. x, fig. 1. 



Since Mr. Page figured Stylonurus Poicriei in 1856, then the only species known, 

 much better specimens have been found, not only by Mr. Powrie, of Reswallie, in Forfar- 

 shire, but also by Mr. Robert Slimon, of Lesmahago, in Lanarkshire. A specimen of 

 another species of this genus, from the last-named locality, furnishes us with most valuable 

 details as to the minute structure of this remarkable generic form. 



Only one specimen of this species from Lesmahagow, Lanarkshire, is known, the 

 intaglio half of which is in the Museum of Practical Geology, Jermyn Street, and the 

 relievo half in the collection of Mr. James Powrie, of Reswallie. It is from the former 

 half that our present figure is taken 2 (PL XXIV, fig. 1). 



The specimen exhibits the carapace and the body-rings as far as the tenth segment 

 united, and one of the long slender swimming-feet in situ on the left side, whilst on the 

 right are seen the bases and portions of two other long appendages. Lying upon the slab, 

 in various positions around the head, are four spiny eight-jointed palpi, or foot-jaws, one 

 of which still retains its attachment to the carapace, although twisted and bent from its 

 natural position. 



Upon referring to the figure of Stylonurus Poicriei in Page's ' Advanced Text-book' 

 (3rd edit., p. 190, fig. 1), it will be seen that it has two pairs of long slender swimming- 

 feet upon either side of the head. In the species here figured, from Logan Water, there 

 is also evidence of a second pair of long limbs, making, with the spiny palpi, four pairs of 

 appendages ; the fifth and absent pair being, no doubt, the antennae, which, as in Slimonia 

 and in Eurypterus, were probably much smaller {ante, p. 109, Fig. 31, et infra, p. 142, 

 Fig. 44). The form of the carapace in Stylonurus is well marked, and very different from 

 any other genus in this singular family. 



In the Logan Water shales, although the finest and most delicate markings are often 



1 See Dr. Hooker's Memoir on "Vegetation of the Carboniferous Period;" 'Mem. Geol. Surv.,' 1848, 

 8vo, vol. ii, part ii, pp. 417, 432, &c. 



2 We figured Mr. Powrie's specimen in the 'Geological Magazine,' 1864, vol. i, pi. x, fig. 1. 



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