CALLOPORID.E. 41 
size slowly, and this causes a transverse section to show two well-defined sets of tubes, 
the large set circular, representing the zocecia of normal size, and the small of angular, 
variously shaped cells indicating zocecia in different stages of development. This latter 
character enables one to distinguish a Callopora by merely examining the end of a branch 
with a lens. The size of the matured zocecia and the shape and number of those still 
developing are often good specific characters. 
The Silurian species of Callopora differ from the numerous Ordovician forms in having 
unusually large, conspicuous zocecia. This characteristic pertains to all of the Calloporas 
known in these strata with the exception of a new species found in the Clinton at Hamilton, 
Ontario, which is of the Ordovician C . ramosa type. For the purpose of comparison these 
large-celled forms may be divided into two groups, the first typified by the genotype 
C. elegantula Hall and the second with 0. magnopora Foerste as the representative form. 
The first group is characterized by large rounded zooecia with numerous mesopores, and 
includes, besides C '. elegantula, C. perelegans Hall from the New Scotland beds of New York, 
C . nana Nicholson from the Wenlock of England, and a few undescribed species or varie- 
ties closely related to the genotype. Of the second group, only C. magnopora has been 
described. C. clausa, a new species" described in this paper* belongs to this section, while 
at least one undescribed form is known. The peculiarity of the group is that at the surface 
the mesopores are reduced almost to a minimum 7 the zooecia as a result being angular and 
contiguous. 
Callopora elegantula Hall. 
PI. XVII ; figs. 11-15; PL XXVI, fig. 12. 
Callopora elegantula Hall, Nat. Hist. New York, Pal. II, 1852, p. 144, pi. 40, figs. la-m. 
Callopora elegantula Ulrich, Jour. Cincinnati Soc. Nat. Hist., V, 1882, p. 250, pi. 11, figs. 0-0b. 
Callopora elegantula Grabau, Bull. New York State Mus., No. 45, 1901, p. 167, fig. 67. 
This beautiful species well deserves to be the type of the fine genus Callopora. The 
species is widely distributed geographically and is easily recognized. Professor Hall 
l figured the macroscopic characters quite fully and later Mr. Ulrich gave views of the internal 
| structure. The following description sums up the specific characters: 
Zoarium ramose, of frequently branching stems 3 to 5 mm. in diameter; surface smooth, 
the maculae distinguished by the presence of zooecia slightly larger than the average and 
of mesopores more abundant than usual. Zooecia thin walled, rounded, 4 to 5 in 2 mm., 
separated by a variable number of angular, thin-walled mesopores, which are often numer- 
ous enough to isolate the zooecial tubes. Zooecial apertures closed in the perfect state by 
.! ornamented covers or opercula having a central circular perforation with a diameter about 
two-fifths that of the zooecia. Six to eight well-marked ridges distributed at equal distances 
from each other radiate from the central opening to the margin. 
Tangential sections bring out the circular thin-walled zooecia separated by the numerous 
angular mesopores of variable size and shape. Because of the numerous mesopores the 
dark divisional line between adjoining zooecia is seldom observed. The striking feature of 
vertical sections is the difference in tabulation between the zooecial tubes and the meso- 
pores. In the early stages of the zooecia the diaphragms are closely set and continue so 
until the tube has reached the normal diameter. Then diaphragms are inserted at intervals 
of about a tube diameter until the peripheral region is reached, when they become more 
ibundant again. The mesopores, which are developed only in the peripheral region, are 
'losely tabulated, two diaphragms usually occurring in a space equaling the mesopore's 
liameter. The tabulation of the mesopores and of the early part of the zooecia is identical 
md it is probable that these two regions were occupied by similar zooids. Transverse 
'.ections show the usual two sets of zooecia, the one, large and rounded, representing the zooecia 
hat have reached the normal size, and the other, small, unequal, and angular, representing 
he younger zocecia in various stages of development. 
No difficult} 7 will be experienced in separating Callopora elegantula from all associated 
'ryozoa, the small, rounded stems with large, circular zooecia and numerous mesopores 
making the species easy of recognition. The new species next described as C. clausa has 
I 
