32 Alexander Petninkevitch, 



1. P. itiDicius Tl). and L., K. Svensk. \'et. Ak. Handl., \'()1. 21, No. 9. 

 1884, pi. I. Pocock, 0. J. M. S., 1902, p. 296. Fritsch, Pal. 

 Arachn., 1904, p. 63, fig. yS. 



From the Silurian (Wenlock) of Gotland. 



2. P caledonicus Hunter, Trans. Geol. Soc. Glasgow, \'ol. Mil, 

 1886, p. 169. Id., Ibid., Vol. V, 1887, pp. 185- 191. Peach, 

 Nature, Vol. XXXI, 1885, p. 295. 



= P. hunteri Pocock, Q. J. M. S., 1902, p. 291, pi. 19. Fritsch, 



Pal. Arachn., 1904, p. 63, fig. 79. 

 P. caledonicus Bather, Ann. Mag. Nat. Hist., (8), Vol. VIII, 1911, 

 p. 676. 



From the Silurian (Ludlow), of Scotland. 



3. P. loudonensis Laurie, Trans. Roy. Soc. Edinb., Vol. XXXIX, 

 1889, p. 576, pi. I, fig. I. Fritsch, Pal. Arachn., 1904, p. 64, fig. 80. 



Found in the Silurian of Scotland. 



Genus Proscorpius Whitfield 1885. 



Genotype and only species P. osborni Whitf., Bull. Am. Mus. Nat. 



Hist., 1885, Vol. I, p. 181, pis. 19 and 20. Clarke and Ruedmann, 



EurypteridaofNewYork,i9i2,Vol. I, p. 387, ff. 81— 83, Vol.11, pi. 88. 



From the Silurian (Cayugan series, Bertie formation), Water- 



ville, N. Y. 



SUB-ORDER DIONYCHOPODA 

 Scorpions with two claws at the end of each tarsus. 

 Pocock in his monograph proposes to divide this sub-order into 

 two groups: Lobosterni "with bilobed, posteriorly laminate sternal 

 plates on the opisthosoma and skeletal plates, whether belonging to 

 the fourth leg or not, on each side of the genital operculum," and 

 Orthosterni, with plates similar to those in recent scorpions. To the 

 first belong the genera Eobuihus and Isobuthus, to the second Cycloph- 

 thalmus, Archaeoctonus, Anthracoscorpio, Microlabis and possibly 

 Palaeomachus. It seems to me, however, that the two groups of 

 Pocock are artificial inasmuch as the new genus Palaeobuthus des- 

 cribed below, although agreeing in the character of its sternites with 

 recent scorpions, is closely related to Eobiithus and Isobuthus in the 

 structure of the coxae. I propose therefore to divide the palaeozoic 

 Dionychopoda into families without reference to the shape of the 

 abdominal sternites. 



Family Isobuthidae. 

 Late Palaeozoic scorpions in which the coxae of the fourth pair of 

 legs are abutting against the genital opercula. To this family belong 



