ANNULOSA : CRUSTACEA. 21 1 



5. The presence of a long, sword-shaped telson, or tail-spine, 

 articulated to the dorsal shield. 



The larval Limulus does not possess the ensiform post-anal 

 spine of the adult 



SUB-ORDER 2. EURYPTERIDA. " Crustacea with numerous, 

 free, thoracico-abdominal segments, the first and second (?) of 

 which bear one or more broad lamellar appendages upon their 

 ventral surface, the remaining segments being devoid of appen- 

 dages; anterior rings united into a carapace, bearing a pair 

 of larval eyes (ocelli] near the centre, and a pair of large, mar- 

 ginal, or sub-central eyes ; the mouth furnished with a broad 

 post-oral plate, or metastoma, and five pairs of movable appen- 

 dages, the posterior of which form great swimming feet ; the 

 telson, or terminal segment, extremely variable in form ; the 

 integument characteristically sculptured." (Henry Wood- 

 ward.) 



The Eurypterida are all extinct, and are entirely confined to 

 the Palaeozoic period. Many of them attained to a compara- 

 tively gigantic size; Pterygotus Anglicus (fig. 67) being sup- 

 posed to have reached a length of probably six feet. In their 

 characters they present many larval features ; resembling the 

 larvae of the Decapoda especially in the fact that all the free 

 somites of the abdomen (except the two anterior ones) were 

 totally devoid of appendages. 



CHAPTER XXXIV. 

 MALA COSTRA CA. 



SUB-CLASS IV. MALACOSTRACA. The Crustacea of this sub- 

 class are distinguished by the possession of a generally definite 

 number of body-segments ; seven somites going to make up the 

 thorax, and an equal number entering into the composition of 

 the abdomen (counting, that is, the telson as a somite). The 

 Malacostraca are divided into two primary divisions, termed 

 respectively the Edriophthalmata and the Podophthalmata ac- 

 cording as the eyes are sessile, or are supported upon eye-stalks. 



DIVISION A. EDRIOPHTHALMATA. This division comprises 

 those Malacostraca in which the eyes are sessile, and the body 

 is not protected by a carapace. It comprises the three orders, 

 Lamodipoda, Isopoda, and Amphipoda. 



ORDER I. L^EMODIPODA. The Lczmodipoda are small Cms- 



