48 Description of Genera and Species. 



keels having their origin in two knobs pass forward from near tlie base line convergently 

 to the tip. The seven last trunk segments form complete rings as in the other species, and 

 are either loose or only imperfectly fused together, their lines of demarcation being 

 perfectly distinct. In fig. 5, where the carapace is tilted up in the manner already 

 described, and especially where, in addition, it is partially removed as in fig. 1, these are 

 seen to decrease rapidly in size when followed forwards from the hindmost one, which 

 can be seen from fig. 4 to have been usually left bare or onlj' covered l)y the posterior 

 lappets of the carapace. 



The tail is seen to be massive and muscular, with each segment well facetted for 

 rolling, and supplied with the usual large subquadrate epimera with rounded anterior 

 angles, almost straight external margins and pointed posterior angles, each fitting on to 

 and overlapping its successor in the most perfect manner, reminding one very forcibly of 

 the similarly ftjrmed tail segments of the recent Squillid, Gonudactylus chiragra Latreille, 

 a drawing of which, natural size, for comparison, is shown in pi. vii., fig. 6. A small spine 

 is seen on the mid-line near the posterior margin on the last two tail segments in fig. 1 and 

 on the last tail segment in fig. ."). These seem to be representative of the median keel seen 

 in P. parki and other forms. The sternites belonging to these six segments are seen in 

 fig. 3, natural size, to be very strongly constructed, with the usual straight articulation in 

 front in the first five segments and deeply emarginate posteriorly, and perforated with 

 large pear-shaped articulations for the attachment of the basal joints of the ])leopods. 

 pi. vii., fig. 7, also natural size, is the tail of Gonodactylus chiragra drawn in the same 

 position for comparison. In the sixth segment the articulations for the uiopods are 

 carried backwards and outwards to the posterior angles, so that the sternite forms a 

 floor across the greater part of the underside within the epimera. The telson, best pre- 

 served in figs. 3-5, is seen to be shield-shaped and elongated, with median crest and 

 long hastate spine behind the articulations of the accessory swimmerets. The outer 

 edge of the telson was evidently set with a row of setaj or short spines, as the articula- 

 tions for them have been observed in specimens from which fig. 5 is taken. The 

 telson was supplied with articulated spines at the constrictions, which are evidentlv 

 the keels of swimmerets. 



The eyes are stalked and moderately large, and were in life probably partially 

 covered by the expanded portion of the rostrum (figs. 1-4). The peduncle of the 

 antennules is short, and does not reach to the tip of the rostrum (fig. 4). The 

 antennual scale is short, leaf-like, and pointed (fig. 4) as in P. jmrki, and the Hagellum 

 more massive and longer than either of those of the antennules. The large body of the 

 mandible is shown as usual by the collapse of the overlying carapace, but the palp has 



