226 i;. ]. I'OCOCK. 



I. The structure of the eutosteniito in the Xiphosurae^ 

 ScorpioiieSj Pedipalpi, Aranea3, iind Solifugfe. 



1. The eutosternite of the Xipliosane, p. 226. 



2. ;, ,, „ Scorpioues, p. 227. 



3. „ ,, J, Pedipalpij p. 231. 



4. ,, ;, ,, Araiiete, p. 233. 



5. The "so-called" eutosternite of the >Solifiig«_, 



p. 237. 



II. The cotnpai'ative inoi-pliology of tlie eutosternite, 

 p. 239. 



III. Tlieories of the origin of the entosteruite, p. 247. 



I. Structure of thk Entosteiinite in the Xiphosuk.Ej 

 Scorpion i';s, Pedipalpi, Arane.e, and Solifug.e. 



1. The Eutosternite of the Xiphosurte. 



The form and structure of the eutosternite in the Auiei'icau 

 Limulus is well kuowu, thauks to tlie fig'ui'es and descriptions 

 of it published by Hay Ijaidcester (5, 6) and ]5en!iaui (2). 



It is a longitudinally oblong plate, with a pair of stout 

 anterior bars, or cornua, forming the pharyngeal notch, two 

 pairs of long and slender apophyses behind the anterior bars, 

 diverging nearly at right angles from the main body of the 

 plate, and a stout but short apophysis springing transversely 

 from its postero-lateral angle on each side. There is also an 

 irregnlar-shaped posterior median process, as well as a pair 

 of short apojdiyses jirojecting subvertically beneath the 

 latter. In the Moluccan species T. gigas (= moluccanus), 

 as was shown by Van der Iloeveii, thei'e is only a single 

 long apophysis projecting from the lateral border in front. 

 This represents the auterior of the two that are found in this 

 ])osition in X. polyphemus. This peculiarity obtains also, 

 1 Iind, in the other Asiatic species, Tachypleus triden- 

 tatus (= longispiua) and Carcinoscorpius rotuudi- 

 cauda, thus confirming the opinion I have already put 

 forward ('Ann. Mag. Nat. Hist.,' A\n-\\, 1902) that these 



