Description, of Genera and Species. 41 



lig. ()), l)ut this undoubted likeness is only seeniiug, and no more indicates close 

 relationsliip than does the likeness <.)i Anthrapakemon io (Talathea. It more probably 

 points to the two forms having to assume a certain shape to suit similar conditions of 

 environment. The specimen also shows that this form was supplied with forwardly- 

 directed massive legs with one of the joints much longer than the rest and bent 

 upwards or forwards. These are too much crowded together and too imperfect for their 

 exact character to be made out ; but they are sufficient to show that tliey are similar to 

 the limbs found in other species of the genus. Fig. 2, also natural size, shows, 

 better than has yet been seen, the details of the tail fan of a still larger individual than 

 that just described. Fig. 5, natural size, shows better than in the former specimen the 

 nature of the long joint of the leg with a short joint interposed between it and part of 

 another where the limb flexes sharply and folds upon itself as in the recent Anaspides 

 and other species of this genus. It also shows the movable leaf-like rostrum, the 

 longitudinal keels on tlu' carapace, and the suggestion of a l)ackwardly-directed spine in 

 the mid-line of its posterior margin. This point, however, was well shown in the 

 original figured specimen. In the original description it was left doubtful as to there 

 being an antennal scale. Fig. 3, also natural size, shows not only the movable rostrum, 

 the stalked eyes, the antenuule ; but sets to rest this doubt, as it shows a short, broad 

 leaf-shaped pointed scale furnished with an external spine. Fig. <i is from a well- 

 preserved specimen not wholly flattened. This shows a point that was missed in the, 

 original description, or rather shows that a misstatement was then made, viz., '• that 

 none of the ridge keels are continued on to it," referring to the area of the carapace 

 in front of the cervical fold. Traces of two short remains of lateral keels occur in the 

 area in front of the fold in places where they are usually found in Anthrapakvmon and 

 Tealliucaris, and which often end in the oi'bital spine. This small but well-preserved 

 individual helps to show how variable the form is in the present species, the 

 carapace here being broader than long, and the tail is also remarkabl}- broad for its 

 length, especiall}- when compared with fig. I. This feature of variability of proportion 

 is well exemplified in the figures which accompanied the original descri[)ti()n. 



t 



Perimectuiu .s I'AKKi, var. DurMCK'AuiN.vTLs var. now I'l. \'.. lig. C. 



General Descrijition. — Figure (i is drawn natural size from a specimen [)re- 

 served in an ironstone nodule which has evidently formed not long after the 

 embedding of the remains. ;ind has thus prevented them from being crushed and 



' Trans. Koy. 8oc. Eilili., 188'2, vol. .x.x.v.. jil. i.\. 



