688 MR. H. G. JACKSON ON THE 



The original specimens of the Hawaiian Geoligia perkinsi are 

 preserved in the British Museum. An examination of the 

 material shows that any generic distinction based on this 

 character must be abandoned, as the females all have this suture 

 well mai^ked on the second, third, and fourth somites. 



An examination of the single uropod cannot but raise doubts 

 as to the genuine nature of the " joints." These are at most 

 ii'regular intervals, and show under a high magnification no 

 arthrodial modification of tissue such as would be found in a 

 natural structure. 



It is therefore suggested that the segments of the rami were 

 produced accidentally. Among two dozen specimens of Ligia 

 exotica — a species distinguished by the length and slenderness 

 of the uropods — I found two specimens which showed "joints" 

 in the rami, identical in every respect with those of Geoligia 

 perkinsi Further, when placed side by side with a uropod which 

 had been purposely bent, no difierence could be detected. The 

 probability that the jointed uropod of Geoligia is of accidental 

 origin is therefore exceedingly strong, and the last anatomical 

 difference between Geoligia and Ligia is thereby removed. 



If G. siinoni and G.pe^'kinsi are compared, it will be found that 

 they differ widely from one another in i-elative size of eyes and 

 head, length of antennas, shape of telson, and other points. The 

 artificial nature of the genus is shown by the fact that they differ 

 more from each other than each differs from certain species of 

 Ligia, and difficulty arises in finding not generic but specific 

 differences between these species and various species of Ligia. 



In 1915, Pearse (p. 549) described under the name of Ligyda 

 richardsonce, specimens he collected in Cincinnati, Colombia, at 

 3800 feet elevation. This species greatly resembles Geoligia 

 simoni, and occurs at no great distance from it, and it is very 

 probable that collection of more material from Venezuela and 

 Colombia will show that both must be referred to the same 

 species. If habitat is to count for everything in the delimitation 

 of genera, then Pearse should have made a new genus for 

 L. richardsonce or have placed it in Dollf us's genus, of which he 

 seemed unaware. His action in retaining the genus Ligia 

 for his new species supports my contention that bionomical con- 

 siderations should have no weight in the separation of this genus 

 from Ligia. 



It may be assumed that these three species have arisen from 

 littoral species of Ligia which have migrated inland and become 

 slightly modified in so doing. Thus Geoligia perkinsi is almost 

 identical with the littoral L. haivaiensis, but G. simoni and 

 L. richardsonce present a more difficult problem, as the adjacent 

 littoral species that have been recorded (L. hcmdiniancc and 

 L. olfersii) do not bear any obvious relation to them. Either 

 they are modified from the haudiniancij or from an unrecorded 

 New World species resembling L. italica, from which they can 

 only Avith difficulty be distinguished. 



