50 Descrijytion of Genera and Species. 



group. This is now made certain by obtaining a specimen showing the carapace (fig. 

 8) and another, fig. 10, which shows the stalked eye, the antennules and antennas, 

 which, though now detached, evidently belong to the same individual as the tail. The 

 specimens are much more fragmentary than those- usually found in the scorpion bed, 

 doubtless pointing to longer exposure before becoming embedded. 



Speci/ie Characters. — Moderately large forms with plain unkeeled carapace. Long, 

 slightly tapering tails with median spine on last three segments. Telson long and 

 narrow, with median longitudinal embossed sword-shaped area continuous with the 

 hastate elongated spine. The external branch of the uropods about same length as telson. 



General Description. — The carapace is of the usual form, but somewhat narrower 

 anteriorly than posteriorly, and a little broader than long, without keels and with only 

 the thickened border. There is a distinct cervical fold. The rostrum is leaf-shaped 

 and jjrobably movable. The sternites of the last trunk segment are wide; those in front 

 become narrower and narrower in rotation. The last trunk segment is seen (fig. 9) 

 to have parted from its fellow in front, and to be still attached to the tail, showing that 

 it was either quite free or incompletely fused to the other trunk segments. The tail is 

 elongated, but is not twice the length of the carapace. It has but slight taper, and is 

 constructed on the usual lines of the members of the genus. The epimera are very 

 strongly developed and are almost square. As usual, they are margined along their 

 anterior and part of their inferior edges by the usual thickened band, ending in the 

 backwardly-directed spine (fig. 12), and are well facetted for rolling. Tlie last three 

 segments have a backwardly-directed spine in the mid-line of the back near their 

 posterior margin. On the fourth segment the spine is little more than suggested. On 

 the fifth it is more pronounced, and on the sixth it becomes still more elongated. The 

 under view of the tail is shown in fig. 8, where the creature is fossilised lying on its 

 back. The square epimera are doubled down and partly conceal the sternites, which 

 are seen to be strong and massive, and with their centre somewhat embossed or keeled 

 and the triangular side portions pierced for the articulation of the pleopods. The fifth 

 segment is slightly displaced. The sixth segment shows the track of the gut, which is 

 evidently distended. The telson is, however, the organ which distinguishes this species. 

 It is of the usual heart or shield shape, and constricted at about half its length for the 

 articulation of the swimmerets, beyond which it is produced into the usual terminal 

 spine ; but in this species the spine is seen to be the extension beyond the body of tlie 

 telson of an embossed median area like the xyphium of the old leaf-shaped cut and 

 thrust sword, the manubrium being broken off. It is this likeness to a sword that has 

 suggested the name. 



