78 



Guide to the Invertehrata. 



Crustacea, and maxilloe, the terminations of which become walking or 

 GALLERY swimming legs, or organs of prehension. The Merostomata include 

 East Side. ^^^ orders, namely, the Eurypteeida and the Xiphosuea (king- 

 Wall-cases crabs). These are all aquatic, the former being extinct, whilst 

 T^w ^^' ^^^ latter (the king-crabs) are still living. 



cases 1- — The Eueypterida have an elongated flattened form, the 



80-82. body tapering towards the tail and having a peculiar scale-like 

 ornamentation upon its hard covering. The head-shield bears 

 a pair of compound eyes, and two minute ocelli on its upper 

 surface, and covers only the mouth with its large lower lip 

 {metastoma) and five pairs of jaw-feet, which are also the only 



Fig. 138. — Limulus polyphemus, Latr. Eecent: North America, a, dorsal 

 aspect of shields ; b, ventral aspect, showing appendages and branchial lamellae. 



locomotory organs. One or more of the segments, which follow 

 next after the head, usually bear divided lamellae, covering the 

 gills, attached upon their under surface ; the other nine or ten 

 segments are without any appendages ; and the body terminates in 

 a spine-like or paddle-shaped telson (Fig. 137). The Eurypterida 

 — represented by Pterygotus, Slimonia, Eurypterus^ Stylonurus, 

 Semiaspis, etc. — appear first in the Silurian (Upper Llandovery), 

 and are represented in the succeeding Devonian rocks, and on into 

 the Lower Carboniferous epoch. The largest forms have been met 

 with in the Old Eed Sandstone of Forfarshire, some attaining nearly 

 six feet in length. (See Table-case 80 and Wall-cases 13, 14.) 



