1889-] On Variation. 1083 
has been continued, and new genera and species have been pro- 
posed, until the group has assumed such vast proportions, and 
contains such a mixture of forms, that it has become almost un- 
manageable. As an illustration of this fact it is observed that in 
a late work (North American Palaeontology, by S. A. Miller), of 
the genera containing species that have been, and are still by 
some, referred to the Monticuliporoids, twelve are placed with 
the Ccelenterata, and nineteen with the Polyzoa. 
The family as a whole is really a natural one, but it is also 
very diversified. It contains species which are massive, frondose, 
discoid or free, parasitic, and ramose. The division into the nu- 
merous genera has been based mainly upon internal structure. 
This, like the external form, is variable, and the one frequently 
bears no relation to the other ; so that a massive form may have 
the interior of a ramose species, or a discoid be like a parasitic 
species. In reading the endeavors to divide the group up into 
families, genera, and species, we are struck by the enormous diffi- 
culty encountered. This cannot be better illustrated than by an 
extract from a lately published paper (Micropalaeontology of 
Canada, Part II.), changing the language so as to make it less 
env^olved, but not altering in the least the sense of the author. 
In this paper it is is said : 
" The genus Diplotrypa, as now understood, embraces at least 
three small but well-marked groups of species, indicating rela- 
tions to widely different families. The typical section bears a 
resemblance to true species of Monotr>'pa that may amount to 
affinity. Monotrypa comprises two very different sections, some 
being true Amplexipordae with relations to Leptotrypa, while the 
typical section presents no very great affinity with any family. 
" Batostoma, which has given no little trouble to place, is more 
intimately related to the typical sections of both Diplotrypa and 
Monotrypa than any of the others. The obvious relationship 
between the three groups suggests the erection of a new family, 
Diplotrypa being the type. By establishing this new family three 
troublesome genera are satisfactorily placed. But with this happy 
result comes another less fortunate, viz., are construction of Diplo- 
trypa and Monotr>T)a. Thus the second section of Diplotrypa 
