NORTH AMERICAN EARLY TERTIARY BRYOZOA. 
71 
Family . — All the species which have the same larval form have the same 
lineage and belong to the same family ; therefore the family is characterized by its 
larval system. The ovicell in which the larva develops is necessarily in rapport 
with it, and a knowledge of its structure gives the essential characters for readily 
interpreting the physiological utility of the morphological and skeletal variations. 
Genus . — A really natural genus differs from another genus only in possessing 
a different function and not in the different form of any skeletal part. The essential 
functions common to all bryozoa without exception are : 
1. Passage of eggs and escapement of the larvae (=rapport of the operculum 
and the ovicell). 
2. Hydrostatic system and extrusion of the polypide (=form of the aperture 
and rapport of the operculum with the compensatrix) . 
3. Calcification and chitinization (= nature of the skeletal part and of the 
frontal considered as immediate deposits of the endocyst). 
All of these functions are indispensable. We combine them in such a way 
that all the species of a genus have the same essential functions. 
We have rigorously followed this principle in the establishment of our new 
genera; we have also modified the descriptions of the described natural genera 
which were often incomplete. 
Evidently often the form indicates the function; for example, the form of 
the aperture reveals the hydrostatic function, the presence of the cardelles indicates 
the movements of the operculum, the presence of a lyrula indicates the nature 
of the operculum, etc. But there are some morphologic variations without 
generic importance which may be common to numerous species; for example, nature, 
form, and attachment of the costules, granulations, and pleurocystal pores, form 
of the zooecium, presence of a rhamma, angle of divergence of zooecia, etc. These 
are the characters of adaption and are not the immediate result of essential 
functions. 
A genus containing species combined only by the identity of characters of 
adaptation is not a natural one. 
The function of the avicularia-ancl onychocellaria is not known, but it can not 
be common to all bryozoa since many species are deprived of these structures; 
they therefore can not furnish good generic characters. Nevertheless, there are 
some groups in which their presence appears to be absolutely indispensable to the 
life of the zoarium and we have therefore considered them sometimes in our 
generic diagnoses. We are not certain that we are in the right path, but in the 
actual state of nomenclature such hesitation is permissible; moreover, the num- 
ber of the genera to be suppressed is not considerable if in the future we should 
not be justified. 
Species . — All the morphological variations and all of the characters of adaption 
are specific characters. They are always utilized without method because we are 
ignorant of the life of bryozoa. 
