362 
SIPHODICTTUXr. 
a series of fine canals, which form pores on the onter surface.*^ 
These canals may unite with one another, but apparently are 
not connected with the cavities of the zooecia. They are mural 
caxuties, described by d’Orbigny as ‘pores intermediaires,’ and by 
Pergens as ‘ cavites intersquelettiques.’ The}' may be regarded as 
branched macula}.^ 
The Hornerida) date from Cretaceous times, the oldest genus 
being Siphodictijum. The most primitive genus is PJiormopora, 
which, as the cpitheca is rudimentaiy, accordingly presents a con- 
siderable resemblance to FilisjJarsa in the Diastoporidan series. 
Some of the species referred to Filisparsa may, in fact, be primitive 
forms of Fliormopora. 
In most Hornerida) the epitheca covers also the obverse face 
of the zoarium. But there is considerable variation in this 
respect, even in the limits of the same genus. Thus, the recent 
Hornera lichenoides (L.) has the obverse face buried by a fibro- 
reticulate epitheca ; whereas in II. violacea^ Sars, the obverse face 
is hare. 
SIPHODICTYUM, Lonsdale, 1849. 
[Foss. Zooph. Atherf. : Quart. Journ. Geol. Soc. vol. v. p. 94.] 
SYXoyTxrs. 
FlUcavea, d’Orbigny, 1854. 
Hornera, pars, von Zittel, 1880. 
Diagnosis. 
Horneridae in which the epitheca on the reverse side is thick. 
The apertures are in irregular transverse series. The maculae 
occur in single or double longitudinal series below the 
aperture. The reverse side is ornamented by ridges, which 
may be reticular. 
^ These mural canals must not be confused with the apparently similar canals- 
traversing the lateral Avails of Fetecava (see Fig. 16, p. 195), which are normal 
zomcia. 
“ Gregory. “British Pahnogene Biwozoa”: Trans. Zool. Soc. vol. xiii. pt. 6- 
(1893), p. 221. 
