srii-l'LARS I 



MEKOSTOMATA 



077 



bent under so as to cover m.,iv than on. --half of th.- \. nn.il -MI- face, Eyes large, 

 approximate, sometimes .surrounded by strong orbital ridgrs ; ""-Hi <>n the slope of a 

 median ridge. Preoral appendages kn.\\u nly by fragment.. .,-. Of th,- 



five pairs of postoral appendages, tin- lir-t is . -In-hit.-, tin- n.-.\t t\\o an- -li.,it, and each 

 joint bears a pair ..f lam. -liar processes. The last two pair- an- .in.niu.n-ly . lougated, 

 nine-jointed, extruding almost to the end of the telson, and t.-rminai.- in I 

 Number of aMominal .-egim-nt.- believed t. In- the same as in Knr ; ii>trriu; each <!' the 

 posterior .segments sometimes l>car a pair of detachable pr.H-i--.-i- ..r .-pini.-i.i. Telson 



FIG. 1422. 



Slimonia acuminata, 

 Walter. Devonian ; Lanark- 

 shire, Scotland. Restora- 

 tion of ventral siirtao-, 

 showing legs I. VI. and 

 abdominal segments VII. 



!'[<;. 1 I'. 1 :'.. 



Pterygotui - lunidt. Silurian; U.Mit/.ikMll, Island .: 



XIX. The first rive of the stm-atii'ii ut' v.-ntral suitacc. ,t, K])istnina ; .. M.-tast.iina ; oc, K\---: I. \'i.. 

 latter with branchial AppMtdaatt. with juints Dtmibend serially in the jwworful swimmr 

 lamellae. 1/7 (after Laurie). I'. \"., 7', First six alxluminal segments. '/:j (:itT F. Schniidtjt 



long and slender. Silurian and Devonian; Scotland. Upper Devonian ; New Y..rk 

 and Pennsylvania. 



Pterygotus, Agassiz (Figs. 1423-1425). Gigantic Eurypterids, attaining a length 

 of over 2 m. Ceplialothorax semicnate, with anterior marginal eyes and central 

 ocelli. Comb-like organs are present beneath the cephalothorax as in Glyptoscorpitu. 

 The metastoma is a heart-shaped plate attached along the middle line to tin- v.-ntral 

 wall of the cephalothorax, between the liases ol' tin- last pair i' l.-.vrs and ext-nding 

 outwards and forwards so as to enclose the jaws in a kind of chamber. Epistoma a 

 thin semicircular plate, occupying the same position as hypostoma in Trilobites, and 

 having the preoral appendages attached close t its posterior border. The latter are 

 large pincers, probably prehensile in function ; by Schmidt and Woodward they are 

 represented as many-jointed, but Laurie states them to consist of but three long joints. 

 Behind the mouth are four pairs of slender walking legs, followed by the large 



