32 THORELL & LINDSTKÖM, SILURIAN >SCORPION FROM GOTLAND. 



is horny and like that of scorpions and insects»; but this, liowever, does not prove 

 that they were air-breathing animals, since a great number of Crustacea, especiall}^ of 

 lower types, and even Limulus, have also a chitinous, instead of a calcareous integu- 

 ment. Nothing is known concerning the organs of respiration and the eyes in the 

 species of Glyptoscorpius. They are stated to be provided with two comb-like organs 

 resembling those of the scorpions; but it is not clear, from the descriptions and the 

 figures, whether these »combs" really occupy the same place of the body in Glypto- 

 scorpius as in the latter animals. These combs, however, as well as the shape of the 

 legs provided with two movable claws, which are figured and described by Peach as 

 belonging to Glyptoscorpius^), seem to favour the view that these Arthropods are really 

 land animals and Arachnids, and related to the Scorpions, though they cannot be re- 

 ferred to the same Order. The structure of the chitinous comb-filaraents of Glypto- 

 scorpius is certainly very different from that of the comb-teeth of the Scorpions, but 

 these filaments seem to be still more dissimilar to the membranaceous, highly vascular 

 gill-lamellaj of the genuine Eurypterids"). — 



For the reasons given above, we cannot share in the opinion that the Mero- 

 storns and the Trilobites are Arachnids, but we consider that they are mest closely 

 related to the Entomostraca, especially to the Phyllopoda. Another question arises as 

 to whether the Merostoms and the Trilobites should be separated from the Crustacea 

 as a distinct »Glass»; but on this point we need not here enter further. The Crusta- 

 cea, as this term is generally understood, form no doubt a much more polymorphous 

 group than the other, coordinate Classes of the Arthropoda; and if there be any ne- 

 cessity of dividing it into two or more Classes, the groups in question are no doubt 

 the first that ought to be separated. For the present, however, it may be enough to 

 form them into a Sub-class of the Crustacea, PoGCilopoda (M'Coy) consisting of two 

 Orders: 1. Palseadse (Dalman) Walcott (Trilobites and Hemiaspids), and 2. Giganto- 

 straca (Hackel) Dohrn, or Merostoma [_-mata\ (Dana) Woodw. (Eurypterids or Poma- 

 tostoma^), and Limulids or Xiphura \_-osura\ Gronov.)*). 



') The only extremity (broken at its apex) whicli is left in sitii in tlie specimen of G. perornatus Peach, is 

 placecl so far in front that it seems to belong to the first pair, or at least to that or to the second pair 

 of appendages. It more resembles, however, an antenna or a walking limb, than the mandible or palpus 

 of a scorpion, but it deviates also not a little in shape from the above mentioned legs with Eurypterine 

 sculpture. 



*) Compare the descriptions and figures of these organs in Woodward, Monograph of the British fossil Cru- 

 stacea of the Order Merostomata, p. 67, Pl. XI, figs. 2a and 2b {Pterygotus bilohus Salt., var. crassus), 

 and p: 115, Pl. XIX, figs. 3 and 4 {Slimonia animinata Salt.). 



^) As a Sub-order, the »family» of the Eurypterids may perhaps aptly be called Pomatostoma, a name de- 

 rived from ntö/.ia, a lid, and arc/^ta, mouth, in allusion to the large operculiform metastoma of these 

 animals. As regards the termination of the name, -stoma seems to be more correct than -stomata: conf. 

 aGTOung, ii:Qt'aTO/.ing, etc. 



'') Compare Er. Schmidt, Misoell. Silur. III,ii: Die Crustaceenfauna der Eurypterenschichten von Eootzikiill 

 auf Oesel, p. 45 (Mém. de FAcad. Imp. d. Sciences de St. Pétersbourg, Vlle Sér., XXXI, JVI 5 (1883). 



