On the " Seraphim " and its Allies. 237 



Explanation of Plate of Slimonia (Pterygotus) acuminata, 

 Salter sp. — Fig. A 1. Carapace of S. acuminata, about one- 

 third natural size, showing the sessile eyes at the angles of its 

 anterior margin (the antennules are not clearly to be seen in 

 this specimen) : a, first pair of simple palpi (antennce) ; b, second 

 pair of ditto (mandibles) ; c, third pair of ditto (first maxillae) ; 

 d d, entire swimming feet, with their broad basal joints, whose 

 serrated edges serve the office of maxillce ; e, post-oral plate, or 

 metastoma ; f, thoracic or genital plate, covering reproductive 

 organs, and concealing the two first thoracic segments, with 

 its median lobe (g), which was described as the conjoined 

 epistoma and labrum ; h, i, k, I, third, fourth, fifth, and sixth 

 thoracic segments, the first and second are concealed beneath 

 the thoracic plate (/) ; m, n, o, p, a, r, six abdominal seg- 

 ments. The thoracic segments are broad and short, whilst the 

 abdominal are long and narrow; s, telson or tail-joint; h, a, a 

 small portion of one of the thoracic segments highly magnified, 

 showing the characteristic squamose markings upon its surface. 



Explanation of Woodcuts. — Fig. A. T&ecent Limulus, "King 

 crab " (female) : 1, antennules; 2, antennae ; 3, mandibles; 4, 

 first maxillae; 5, second maxillae; 6 (swimming feet), third 

 maxillae. Fig. B. Thoracic appendage, covering reproductive 

 organs (a). Fig. C. Antenna of a male Limulus (recent). 

 Fig. D. Foot of swimming crab (recent), Platyonichus ocellatus. 

 Fig. E. Thoracic appendage of Slimonia acuminata. Fig. F. 

 Parka decipiens, supposed eggs of Pterygoti. Fig. G. Head of 

 Eurypterus remipes, De Kay (after Hall's figure), under side, 

 exhibiting the organs of the mouth : a, antennule ; b, antennae ; 

 c, mandibles ; d, first maxillae ; e, (swimming feet) second 

 maxillae ; p, post-oral plate, or metastoma ; m, thoracic ap- 

 pendage ; 1, 2, 3, 4, thoracic segments. Fig. H. Upper side 

 of same, showing the eyes, and (6) larval eye-spots. Fig. K. 

 Slimonia acuminata (restored) ; the letters refer to the same 

 parts as in Eurypterus remipes. 



