Elui rack nida — X iphosu ra. 81 



Division B. — Embolobranchia. 



Order 1. — Scorpio)ies (Scorpions). 



,, 2. — Pcdipalpi (Whip-scorpions and thcii' allies). 

 ,, 3. — Palpigradi. 

 „ 4. — Arancac (Spiders). 

 ,, 5. — Solifugac (False Spiders). 

 ,, 6. — Psciidoscorpioncs (False Scorpions). 

 ,, 7. — Podogona. 

 ,, 8. — Opilioiies (Harvest-men). 

 „ 9.— .4cftri (Mites). 

 Sub-class 2.— PYCNOGONIDA. 



Sub-class I— EUARACHNIDA. 



Both the prosoma (" cephalothorax ") and the opisthosoma 

 (" abdomen ") are well developed in these Arachnida and are 

 typically separated from one another by a praegenital segment, 

 which generally disappears, however, in the adult. The prosoma 

 is usually covered dorsally by an undivided carapace which 

 is, however, sometimes segmented posteriorly. Its appendages 

 number six pairs. The first pair (" chelicerae ") are often chelate 

 or prehensile, whilst the second, third, anel fourth pairs may also 

 be chelate, but are usually feelers (palps) or walking legs. When 

 fully developed, the mesosoma consists of six somites, which bear 

 plate-like appendages in the aquatic species ; in the land forms 

 these appendages are much reduced and modified or absent. 

 The metasoma also typically consists of six somites, which are 

 devoid of appendages. The mesosoma and metasoma are often 

 fused to form an opisthosoma or " abdomen," and obliteration of 

 segmentation often takes place. 



The Euarachnida are divided into two Grades : — 



Division K.—DELOBBANCHIA. 



The respiratory organs of the Delobranchia are of an aquatic 

 type, all the^ large plate-like appendages of the middle region of 

 the body (mesosoma), wdth the exception of the first, being 

 furnished with branchial lamellae. There are two orders. 



Order 1. — Xiphosura (King-crabs). 



None of the appendages of the prosoma are paddle-like in 

 form in the Xiphosura. The segments of the opisthosoma do not 



G 



