58 Description of Genera and Species. 



bristles along each external margin. External branch of uropods large and blade-like, 

 and much longer than the internal branch, which is thin and delicate. 



General Description. — The integuments are tliin. The trunk is unknown. 



The tail measures 25-30 mm., and is long and sub-cylindrical and fusiform, 

 tapering backwards from the second segment, which is the largest, to the spring of the 

 basal joints of the uropods on the sixth segment, which is nearly double the length of 

 any of the others. The first five segments bear well-marked epimera, which are 

 obtusely pointed, those of the first segment being considerably shorter than those of 

 the succeeding one and overlapping on to it. Those of the other segments overlap 

 each other in order backwards. There are distinct pivots at the bases of the epimera, 

 and the segments are well supplied with smooth facets for rolling. The epimera of the 

 sixth segment are small and only found on the anterior part. 



The telson is much shorter than the external branch of the uropods. It is tumid 

 at the base and flattened behind. A median groove commencing in the tumid portion 

 is extended into the flattened termination, causing the tail to be distinctly forked. 

 The two ridges left by this furrow are each traversed by a longitudinal groove, which 

 has a gentle curve outwards and terminates on the exterior margin. The two raised 

 areas are prolonged beyond these grooves and terminate abruptly, forming an 

 articulation for two flattened plates which act as swimmerets. The lateral margins of 

 the telson are set with an- even row of strong bristles, and the flattened plates and the 

 fork are fringed with setaj. 



The appendages of the tail (figs. 12, 13) on the first five segments appear to be 

 constructed with very strong muscular basal joints, and to have terminated in at least 

 one branch constructed as a many-jointed swimmeret, but the terminal portions are 

 not sufficiently well preserved to determine whether the inner branch of the anterior 

 pleopods was modified for sexual purposes, or whether they bore the rudimentary 

 gills like those of the males in some of the recent forms ; but the general character of 

 the remains preserved suggests that these pleopods were probably like those of the 

 males in the recent Siriella and Amblyops. The uropods have a flattened subquadrate 

 basal joint, the inner part of which is overlapped by the bulge of the telson when the 

 tail fan is not spread. The external swimmeret is much elongated and blade-like, and 

 tapers to a sharp point, having an elegant double curve, first outwards and then 

 inwards as the tip is approached. It is strengthened exteriorly and traversed 

 throughout the greater part of its length by a double fluting. Its inner edge is thin 

 and fimbriated. It therefore bears a stroncr resemblence to an Eastern stabbinw-knife. 

 It was evidently set with strong seta3 along its inner margin. There appears to have 



