CLASSIFICATION PYCNOGONIDA. 781 



belong to the Scorpionidea and are found in the Silurian deposits ; 

 spiders and Pedipalpi are also Palaeozoic but do not occur before 

 the Carboniferous. 



The following classification of Arachnida is adopted in this 

 work : 



Sub-class I. PANTOPODA (p. 781). 



Sub-class II. MEROSTOMATA (p. 785). 



Order (i) Xiphosura (p. 786). 



Order (ii) Eurypterida (Extinct, p. 796). 



Sub-class III. EUARACHNIDA 



Order (i) Scorpionidea (p. 798). 



Order (ii) Pedipalpi (p. 807). 



Order (iii) Araneida. (p. 811). 



Order (iv) Palpigradi (p. 827). 



Order (v) Solifugae (p. 829). 



Order (vi) Pseudoscorpionida (p. 833). 



Order (vii) Podogona (p. 836). 



Order (viii) Phalangidea (p. 837). 



Order (ix) Acari (p. 842). 



Sub-class I. PANTOPODA (PYCNOGONIDA).* 



A peculiar group of Arachnids in which the segments correspond- 

 ing with the meso- and meta-soma (abdomen) have disappeared. 

 The eighth segment that which corresponds with the pre-genital 

 evanescent segment in Limulus and Scorpions exists and bears fully 

 developed legs on which the genital pore opens, though the latter may 

 be repeated on the fifth and sixth and seventh segments. 



The Pantopoda are all marine and are usually found crawling 

 slowly over sea- weed or amongst zoophytes. The body is always 

 small as compared with the legs, and it consists of four regions (Fig. 

 509) . The first of these bears anteriorly the proboscis at the tip of 

 which is the small, triangular mouth. The proboscis is regarded 

 as an outgrowth of the parts surrounding the mouth and it varies 

 greatly in form and size. It maybe almost immovably connected 

 with the prosoma or it may be articulated and so movable. 

 Behind, four anterior, primitive somites are fused to form the 



* Hoek, Challenger Reports, vol. iii, No. 2, 1881. Dohrn, Fauna and 

 Flora d. Golfes v. Neapel, iii, 1881. 



