THE HEDERELLOIDEA — BASSLER 27 



The discrimination of the Reptariidae is dijBicult because a single 

 species presents so many variations in growth. Zoaria growing upon 

 smooth organisms exhibit the size of zooecia and method of branching 

 and budding characteristic for the species, but when, as in many cases, 

 the host presents an uneven, often rough surface, the aspect of the 

 zoarium is considerably changed. Age also has its effect, for the youth- 

 ful zoarium may appear so different from older examples of the same 

 species that numerous specimens are necessary to determine the true 

 specific limits. Fortunately the measurements as to size of zooecia 

 and angle of branching seem to be fairly constant when averages are 

 considered. 



For convenience of description, the following terms are employed in 

 this paper: The zoarium commences with a bulblike ancestrula, from 

 which the initial zooecial tube emerges to give rise by lateral budding, 

 alternating to the right and the left, to the primary branch. This, 

 therefore, consists of individual zooecia springing from about the 

 middle of the side of the preceding tube so that apparently a continu- 

 ous central tube appears to be present. Then after a certain distance 

 characteristic for the species, one of the tubes, branching off at a 

 definite angle, continues to bud in that direction and forms a new 

 branch, which later on will repeat the process until finally the entire 

 zoarium is produced, made up of primary, secondary, and even later 

 branches. Thus, the angle of branching of the zoarium may be dis- 

 tinguished from the angle at which the individual tubes bud, and 

 branching and budding, although based upon the same phenomenon, 

 should be discriminated. With these distinctions in mind, the specific 

 characters then comprise the angle and interval of zoarial branching, 

 the angle and frequency of budding of the individual tubes, the length 

 and width of the tubes, the number of tubes occurring along a branch 

 in a definite distance, their rate of expansion, and their surface orna- 

 mentation. The measurements are computed as follows: The diam- 

 eter of a tube is taken at its distal end, the length of a zooecium is 

 that of a normal bud from a branch, and the number of zooecia in a 

 given length is measured along the same side of a regularly developed 

 branch. The bibliography of this suborder is not large, and it is be- 

 lieved that all references to the literature are cited in the course of 

 this paper. 



The Paleozoic Cyclostomata as well as the Trepostomata in most 

 instances form solid calcareous colonies, grouped together as stony 

 Bryozoa. Special care is necessary in illustrating these Bryozoa, and 

 many articles even of recent date have been published with wholly 

 inadequate illustrations. I have devoted much time to the subject 

 of proper illustration of such fossils, and a grant from the Penrose 

 Fund of the Geological Society of America has enabled me to prepare 



