W. T. CALMAN— CEUSTACEA. 53 



relatively much larger in the small and medium-sized specimens, where they fill, or 

 nearly fill, the orbits ; in the largest specimens the orbits appear much too large for 

 the eyes. The margin of the orbits is a raised line which is beaded only in small 

 specimens. The outer orbital angle projects at most very slightly and is often quite 

 smoothed away ; below it there is usually a small orbital notch, but in some of the 

 larger specimens this can no longer be detected. 



The degree to which the lateral margins of the carapace project beyond the outer 

 orbital angle (a point to which much importance is attached by Miss Rathbun in her 

 revision of the subgenus) varies with the size of the specimen. In all the specimens 

 of 20 mm. carapace-length or less the lateral projection is less than the major diameter 

 of the orbit ; in all the specimens of 25 mm. and upwards it exceeds that diameter. 



On the under surface of the carapace the pterygostomial furrow is, at most, indistinctly 

 granulated ; the inferior prolongation of the cervical groove (separating the sub-hepatic 

 and sub-branchial regions) is more or less indistinct, sometimes practically obsolete 

 (as in Hilgendorfs P. Upartitum). 



Text-fig. 10. 



Abdomen of the specimen shown in text-fig. 9. Natural size. 



The groove on the merus of the third maxillipeds varies in distinctness without much 

 relation to the size of the specimens ; it is never very strongly marked and in some of 

 the large specimens it is altogether obliterated. The merus of the chelipeds has its 

 three edges granulated, the granules being most prominent and conical on the anterior 

 edge. The second tooth on the inner side of the carpus is small and is followed on the 

 proximal side by a row of large granules. The chelae are smooth, with faint grooves 

 on both fingers ; the fingers gape to a varying degree in large specimens of both sexes 

 and are generally a little more slender in large males than in females. 



There are two transverse grooves on the sternum of the male in front of the abdomen ; 

 the anterior region of the sternum in females is setose. The male abdomen has nearly 

 straight sides and the angle which the outline forms between the last two segments does 

 not project laterally. 



The two type-specimens of P. johnstoni from Kilimanjaro (which have not hitherto 

 been figured) are males and are somewhat larger (35 and 37 mm. carapace-length) 

 than any of the Ruwenzori specimens. They agree with the latter in the general 

 characters of the "^jer^«^?(s-group " as defined by Miss Rathbun (t. c. p. 162) and in 



