190 DIPLOPODA. 
appearance, which suggested to Saussure the name “ /imax’’ for the typical species of 
the genus. Yet, despite the variation in these and other respects, the general type 
of phallopod remains constant in all the Central-American representatives ; and the 
spine on the apex of the second segment of the leg is never wanting, though variable 
in size. 
With the material at my disposal I have found it impossible to write a monograph 
of the members of this genus. ‘This could only have been done if specimens of all the 
described species had been available for examination. The species themselves are 
not difficult to distinguish, as a rule, by eye, but the differences between them are in 
many cases extremely difficult to express intelligibly in writing; and I have found it 
practically impossible to enumerate succinctly the distinguishing features of both sexes 
of the species in a dichotomous analytical key. 
The majority of those described by Saussure and Humbert I have been compelled 
to omit from the table, because many of the characters I have found useful for 
identification purposes are not mentioned in the descriptions published by those 
authors. Notably have they omitted in nearly all cases to describe the structure of 
the phallopods. 
It is unfortunate that many species have been based upon specimens of a uniformly 
pallid hue, which had either been decolorised by drying or by the action of alcohol, or, 
having recently moulted, had not acquired their natural tints. For it does not seem 
likely that any of the species are normally testaceous when adult in a state of nature. 
The possibility of this being so, however, must be borne in mind. However that may 
be, when a number of species are mixed together it is generally not difficult to sort 
them out by colour alone; and if the colours had in all cases been known, the 
characters they present would have been of the greatest use in drawing up a table of 
distinguishing specific features. As a slight aid to the determination of the species I 
have endeavoured to draw up a supplementary table based upon the pattern where 
this has been preserved and has been recorded :— 
a. Small, length about 20 mm.; keels with anterior border strongly raised, the 
area behind it depressed ; lateral border of keels from about the 5th to the 
15th wider anteriorly than posteriorly, so that the lateral border is inclined 
obliquely inwards and backwards; posterior border thick, a little uptilted 
and deeply notched at base; phallopod with main branch about as long as 
palmar area, somewhat sharply incurved distally; auxiliary branch very 
short, almost spiniform . 
a usillus. 
a’. Larger, length not less than about 27 mm.; keels not noticeably depressed , 
behind the anterior border, which is not markedly raised as compared with 
the lateral border; lateral border not inclined obliquely inwards and back- 
wards, the anterior angle of the keel not projecting more prominently than 
the posterior angle. 
