1960 ] 
Christiansen — Genus Pseudosinella 
3 
Systematic Account: General Discussion 
The genus Troglosinella was created by Delamare for the species 
hirsuta and spinosa. Examination of much more extensive material 
encompassing several new species makes it clear that the generic limits 
set up by Delamare are impractical. Two of the most basic character- 
istics used to separate the genus (the ringing of the fourth antennal 
segment, and the small non-lamellate teeth) are present in some 
forms of hirsuta and absent in others. Beyond this the reduced tooth 
structure of the unguis appears in a number of separate epigeic forms. 
The spines of the dens, also used to separate the genus, are found 
in only one species (P. spinosa ) and the “heavy hairs” found on the 
dorsum of the dens in hirsuta are found in large specimens throughout 
the whole of Pseudosinella. In view of this, and my failure to dis- 
cover any other practical way to separate the genus from Pseudosinella, 
I consider Troglosinella Delamare to be a synonym of Pseudosinella 
Schaffer. It is regrettable that this is unavoidable, since the species 
clustered around P. spinosa do represent an evolutionary unit. 
Ratios and Size 
As with almost all groups of Collembola, the size of the species 
varies considerably. It is extremely risky to determine the size of a 
particular species upon anything except large samples from a variety 
of localities. Time and again a whole sample will be made up of 
small individuals, or will consist exclusively of extra-large specimens. 
With all this in mind it is possible to break the cave species of Pseu- 
dosinella of the United States into three size ranges: small (averaging 
around I mm.) — P. espana (?), P. alba, P. folsomi, P. duodecim- 
punctata, and P. sexoculata ; medium (averaging between 2-3 mm.) — 
P. orba (?), P. boneti (?), P. dubia, P. gisini, P. argentea and P. 
hirsuta ; and finally the large (averaging around 4 mm.) — P. spinosa. 
The ratios of the various organs vary, but if we consider all the 
species, almost any organ ratio can be expressed as a straight line, with 
one or two notable exceptions. The only striking exceptions involving 
several species concern the first and second abdominal segments and 
the length of the antennae. The latter is illustrated in graph 1, which 
shows the most sensitive segment, the fourth, plotted against the 
cephalic diagonal. It can be seen that the most highly evolved cave 
forms develop progressively longer antennae. For most of the other 
organs a single straight line can express the growth changes and en- 
compass all species. Graph 2 shows a summary of such growth lines 
for organs of the various parts of the body. There are a few varia- 
