PLESIOCHACTAS. — MEGACOEMUS. 17 



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I. Plesiochactas dilutus. (Tab. IV. figg. 5, 5 a-f 9 $ .) 



Megacormus granosus, var. dilutus, Karsch, Arch. f. Naturg. 1881, p. 18 l . 

 Plesiochactas dugesi, Pocock, Ann. & Mag. Nat. Hist. (7) v. p. 470 (1900) 2 . 



$ . Colour deep reddish-brown, nearly black, the smooth areas of the carapace reddish ; the terga with a small 



posterior median yellow spot, a much larger yellow spot on each side of this, the series forming two nearly 



complete and uninterrupted dorsal bands ; also a large but not strongly defined yellow spot on the 

 posterior angle ; tail deep red-brown, mottled with black ; sterna deep brown, paler mesially ; chelae deep 

 reddish-brown, fingers blacker with yellow tips ; legs yellow, broadly banded with black ; sternum and 

 coxae yellow, the former and the maxillary processes of the first and second leg partially infuscate ; coxa of 

 chela blackish. Carapace coarsely and sub&erially granular ; a median granular crest running backwards 

 from the ocular tubercle and a series of coarse granules on each side from lateral eyes ; the ocular tubercle 

 with two rows of granules; carapace as long as caudal segments 1 + 2 + I of 3, or as 3 + 4 or 5, a little 

 shorter than the movable finger. Terga finely granular in front, very coarsely granular in the posterior half, 

 not distinctly keeled, except the last, which has four coarsely granular keels, with its median area finely 

 and closely granular. Sterna finely and closely punctured ; the last finely granular, with a single median 

 and an abbreviated granular crest on each side, a few coarse granules on its posterior and lateral margins 

 as well as on the lateral margin of the fourth sternum. Tail between three and four times as long as the 

 carapace ; its third segment as wide as long, fourth one-fourth longer than wide ; fifth nearly or quite three 

 times as long as wide ; all the keels coarsely granular, the inferiors on segments 2-4 posteriorly denti- 

 culate ; upper surface of 1-4 with a median closely granular area ; the lateral and inferior surfaces much 

 more coarsely but somewhat sparsely granular, the inferior surface of the first nearly smooth ; fifth very 

 weakly granular above, with squared, coarsely granular superior lateral edges ; the lateral and inferior- 

 surfaces and the inferior crests granular, as on the other segments ; median lateral keel strong on the 

 first, present on the anterior fourth of the fifth, absent on the other segments ; vesicle granular throughout, 

 except on the normal smooth tracts, piriform, a little wider than high and about as wide as the fifth caudal 

 segment or as the humerus ; aculeus long and lightly curved. Chelae with humerus and brachium coarsely 

 but not closely granular, smooth or nearly so, all the keels coarsely granular, anterior side of brachium 

 with at least two strong teeth ; hand considerably wider than brachium, its width about two-thirds the 

 length of the underhand; furnished with seven granular keels, its upper surface with two granular 

 finger-keels and a keel between them, the area between the keels coarsely but not closely granular ; 

 fingers long and slender, not lobate. Legs with femur and patella granularly crested, femur of third and 

 ' fourth granular on the external surface as well. Pectines with 8-9 teeth. 

 Measurements in mm. — Total length 42, carapace 6, tail 24 ; width of first segment 3, of fifth 2, of brachium 2*2, 

 of hand 3 ; length of underhand 4*8, of movable finger 6*5. 



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Hah. Mexico, Atoyac in Vera Cruz (A. Duges 2 ), Cordova 1 . 



It appears to me to be highly probable that the type of Plesiochactas dugesi, from 

 Atoyac, is conspecific with those from Cordova, which Karsch regarded as a variety of 



Megacormus granosus and named dilutus. These specimens measure 57-65 mm., have 

 8 and 9 pectinal teeth, smooth sterna, no median tergal keel, and no wart-like tubercles 

 between the two inner keels on the last tergal plate. I have also seen a young 

 specimen of this or a nearly allied species from Guatemala. 



MEGACORMUS. 



Megacormus, Karsch, Arch. f. Naturg. xlvii. p. 17 (1881) ; Kraepelin, Jahrb. Hamb. Wiss. Anst. 



xi. p. 151 (1894) j Das Tierr., Scorpiones et Pedipalpi, p. 161 (1899). 



Related to Plesiochactas, and apparently a specialized offshoot of it. Distinguishable by having the carapace 

 narrowed in front, by the reduction in size of the pectines (which is accompanied- by the entire loss of 



biol, CENTR.-AMEK., Arachn. Scorp., August 1902. 



