446 
NEW ARRANGEMENT OF 
it is a single tooth, cleft or divided more or less from the 
apex downwards, sometimes even nearly to the base ; but 
at whatever point the division stops, there is vih line visible 
below that point, by which the separation could be conti- 
nued. The dens fissus is often perforated in such a man- 
ner, as to prove, that^ in many instances, the division is the 
result of a series of iacunee. A dens fissus should be con- 
sidered as unity ; a dens geminatus as a compound. The 
latter might be called dens separahilis^ or dens fissilis; the 
former simply dens fissus^ 
The denies per paria approximati are at no period of 
their growth longitudinally united ; they are understood to 
be always separate, although not equidistant. Thus they 
must not be confounded with the dens geminatus, which is 
often divided to the very base by the linea separahilis. 
To illustrate this a little farther, we will take a peri- 
stome of a Splachnum for examination ; and suppose (as 
often takes place) that two or four of the thirty-two pri- 
mary teeth are united by longitudinal cohesion. These 
teeth we would term uni^ or bi-geminantes ; and the tooth 
formed by this gemination, uni- or hi-geminatus. In seve- 
ral genera, as Splachnum, Ortliotrichum, &c. this structure 
of the teeth forms a leading character*. 
* We are aware, that, in the present state of muscology, we are liable 
to censure for the introduction of new terms and definitions, and the more 
so, that it is extremely difficult to define our ideas in express words. Thus 
several mosses are represented as having a longitudinal line down the middle 
of their teeth, and yet we have several reasons for doubting if they be really 
geminated ; though a geminated tooth may be only partially divided, and is 
marked by a line, still we do not intend to assert, in every case where such a 
line is figured, that the tooth is geminated. It is therefore to be much wished 
that such as make drawings of the peristomes of mosses, would pay parti- 
cular attention to this point. 
