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 and 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. 



