EAELY PALEOZOIC BRYOZOA OF THE BALTIC PROVINCES. 243 



although somewhat diagrammatic views of the internal structure of 

 Eichwald's species (pi. 4, fig. 5), and these, in connection with the 

 original figures, are sufficient for purposes of identification. As usual 

 in tliis genus, and as indicated in the name apphed to the American 

 form, the surface characters particularly are somewhat variable. 

 This variation is mainly dependent upon age. Thus, in Eichwald's 

 figure (fig. 137), the two fragments are of young zoaria in which the 

 zooecia are elongate and separated by similarly elongated, shallow 

 mesopore spaces. The other extreme, that of old age, is shown in 

 UMch's illustration (fig. 138 &). The internal characters are most 

 constant and will serve whenever doubt is raised. 



Ulrich has given a detailed description, from which the following 

 notes are derived : 



Zoarium of ramose branches 2 to 6 mm. in diameter, the younger 

 examples slender and nearly cylindrical, the old ones more or less 



Fig. 137.— Eridoteypa ^dilis. Copies of Eichwald's figures of Cladopora ^dilis. a and c, two 



FRAGMENTS OF THE NATURAL SIZE; 6 AND d, ENLARGEMENTS OF THE SAME SPECIMENS. WESENBERG 

 LIMESTONE (E), WESENBEEG, EsTHONIA. 



irregular. Zooecial apertures variable, the changes due chiefly to age, 

 always oblique, the degree decreasing with age; walls tliick, generally 

 ridge-shaped, and highest posteriorly, sloping gradually down into the 

 apertures. In young examples, also in old ones on which a new layer 

 of zooecial tubes was formed, the apertures may be exceedingly obhque 

 and drawn out anteriorly. With age they became gradually more 

 direct. The arrangement of the apertures is always more or less 

 irregular, some of the short rows having six, others seven, and occa- 

 sionally eight, in 2 mm. Small maculae, either pitted or irregularly 

 sculptured; commonly present in the older examples. In others the 

 maculae are represented by clusters of zooecia which, though a httle 

 larger than the average, are distinguished from them chiefly by the 

 greater thickness of the interspaces. The mesopores too are most 

 variable, sometimes appearing to be wanting over large portions of 

 the surface and at other times twice as numerous as the zooecia. 

 As a rule, however, they are few, appearing at the surface as occa- 



