DICRANACEAR, 333] 
TREMATODON Michx. 
difficulties by no means disappear, as several of the characters relied on, 
such as the length of seta and its degree of flexuosity, the relative lengths 
of capsule and neck, and the development of the struma, are all subject to 
a certain degree of variation. The struma especially depends for its dis- 
in different stages of maturity. 
The most constant and most valuable character, perhaps, resides in the 
peristome, and the genus has been divided by Roth (Aussereuropaischen 
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rds base, by the transverse articulations ; (3) divided—as in (2)—for 
some distance up, then united again in the upper half. 
The type of peristome (3) is found in the greater number of species; but 
there may often be found in the same species, and, indeed, in the same tuft, 
side by side with the normal form, examples where the teeth are much more 
irregular, sometimes split into three divisions, here and there branched, or 
again very irregularly connected one with another. Types (1) and (2) are 
represented by a smaller number of species. 
In a second, lesser group the teeth are much more rudimentary than in 
Eutrematodon, and their very short divisions not united above as in that 
subgenus, but more or less free throughout their length, only connected 
here and there by a few transverse articulations. This constitutes the 
subgenus Pseudomicrodus Roth. 
A small section of Hutrematodon show a slight deviation from the normal 
types of peristome described above, in having the teeth perforated or split 
here and there along the median line from top to bottom. They form, 
therefore, a transitibn, to some extent, between Eutrematodon and Pseudo- 
microdus. 
Finally, a certain number of species have the peristome entirely wanting 
or reduced to the basal cylinder simply—Gymnotrematodon C.M. 
Basing our classification on this structure, we may arrange the New 
Zealand species as follows, affording a fairly practical key to their identifi- 
cation :— 
Subgen. GyMNoTREMATODON C. M. 
1. Trematodon Mackayi (R. Br. ter.) Broth. 
Subgen. PszEupomicropus Roth. 
2. Trematodon flexipes Mitt. 
