262 Memoirs of the Indian Museum. |\'()i. Ill, 



5. THIC VARIABLE SPKCIEvS. 



One of the most striking features of the species of Oriental Passalidae, as these 

 have been defined above, is that a few of them are remarkably variable in size, 

 whereas most are not. The two most variable species are found in the Leptaula- 

 cinae. Thej' are Leptanlax bieolor (length 13-25 mm.), and Leptaulax dentatiis (i9'5-37 

 mm.). Of both of them the largest specimens I have seen are about twice 

 as long as the smallest. Next to these come three species of Aceraiinae, Episphcnus 

 indicHS {25-41 mm.), Episphcnus comptoni (27"5-42 mm.) and Aceraius grandis 

 (northern race, which I have been better able to study than southern one, 33-49 mm., 

 total range of species, including southern forms, 33-54 mm.), of each of which the 

 largest specimens are a little more than half as long again as the smallest. Of the 

 remaining species of Oriental Passalidae none appear to vary in size in any such 

 striking manner; the most variable, as far as my own observations go, are Aceraius 

 helferi (30-40 mm.), Leptaulax humerosus {15-20), Leptaulax planus (11-14 mm.), 

 Pleurarius brachyphyllus (35'5-45 mm.) and Ophrygonius canton {s. lat., 27 34 mm.), 

 of all of which the largest specimens are somewhat more than one and a quarter times 

 as long as the smallest; then come Ceracupes austeni (20-25 mm.) and Tiberioides 

 kuwerti (36-44 mm.), in both of which the largest specimens are just one and a 

 quarter times as long as the smallest ; these are followed by others little less variable 

 than themselves; and so on through all the rest. 



Leptaulacides bieolor, Leptaulax dentatus, Episphenus indicus, Episp'ienus comp- 

 toni, and Aceraius grandis are all common species, so it is natural to suppose that 

 their range of variation may be more completely known than that of other .species, 

 most of which seem to be less abundant. But if this was the real and only reason 

 for their apparently exceptional variability, we ought to find isolated examples of 

 unusual dimensions belonging to at least a few of the many rarer species, and such 

 are not found ; and the comparative uniformity in length of all specimens of the long 

 series I have seen of Episphenus neelgherricnsis, is sufficient to indicate that even species 

 closely allied to those of exceptional variability may be remarkably constant. Tiberius 

 andamanensis and sikkimensis, too, are represented in our collection by uniform series 

 of sufficient size to render it practically certain that these species do not vary in 

 length to any great extent. 



I have examined over a hundred specimens of each of the five variable species, 

 except Episphenus comptoni, of which I have seen only thirty-eight'; so it is not 

 surprising that the continuity of the variation in length of the specimens before 

 me, is much more broken in this species than in any of the others. But for the 

 presence among these of three .specimens from Bulutota, of which one is 275, one 

 30, and one ^y mm. long, all the evidence would point to the species being divisible 

 into two groups distinguished from one another by size alone, in view of which I have 

 thought it best provisionally to describe these groups above under separate names, 

 since names already in use can be applied to both of them. To my mind, however, 



' I have since seen a number of additional specimens. 



