HOr.XERTD.i:. 
361 
Affinities. 
This family is a branch from the Iclmoniidae, clrffering zoarially 
from that group by the arrangement of the zooecia. Instead 
of having the alternate series of apertures characteristic of the 
Idmonids, the apertures are eitlier (j^uite irregularly arranged or 
occur in simple linear series. 
Several authors, including Busk and Pergens, have included 
both Hornerids and Idmonids in one family. But this arrange- 
ment makes the Idmoniidae a very cumbrous group, which is 
(.lifficult of diagnosis. There are several points of resemblance 
between the two families. Thus, comparison of the figure of 
Uoniera lichenoides (L.) with Pig. 16 on p. 195, which represents 
Fig. 44. — Ilornera lichenoides (L.). Recent: Norway. A longitudinal 
section, x 12 clia. 
a corresponding section across Retecava lichenoides (Goldf.), shows 
the similarity of the laminated epitheca in both families. 
In addition to the normal apertures there are in the Horneridse 
two further sets of openings on the surface of the zoarium. In 
some cases, as in JSornera langethali^ there occurs on the reverse 
surface a number of small raised tubuli. These are probably the 
prolongations of rudimentary zooecia, which Pergens has described 
as ‘ canaux de renforcement.’ They are often associated (as in 
Pig. 433) with small depressions, which mark the sutures between 
zooecia. In the section of RLornera lichenoides shown in Pig. 44, 
the lateral and obverse walls of the zoarium are penetrated by 
