ON FOSSIL POLYZOA. 195 
Family V1. Horyerma. 
In founding this family Mr. Hincks says only: ‘ Zowcia opening on 
one side only of a ramose zoarium never adnate and repent.’ (‘ Brit. Mar. 
Polyzoa,’ vol. i. p. 467.) 
Excepting the Siphodictyum of Lonsdale, Hornera, as known to us in 
the Crags, is not represented—typically—below the Tertiaries. I cannot 
therefore accept the types of the recent family for Mesozoic or Paleozoic 
genera. 
Greensand . Stphodictywm gracile, Lonsdale = Hornera (?). 
Family VII. THamniscipa. 
Zoarium forming free dichotomising branches, or pinnated fronds. 
Zoecia on one side only, with from three to five (or more ?) rows of cell- 
openings in a branch, occasionally having a smaller opening above or 
below the peristome of the cell (base of spine ?).! 
Genus Thamniscus, King. 
»  Acanthocladia, ,, ? = Ichthyorachis, M‘Coy. 
These genera, which have heretofore been loosely defined and. as 
loosely accepted by some Palzeontologists, are now restricted. The genus 
Thammiscus was founded by Professor King, and though he did not read 
aright all the characters which his specimens afforded for a complete study, 
still he gave a good general estimate of its varied features. Professor 
King says (‘Perm. Foss.’ p. 44): ‘I formerly placed the type of this 
genus in Lamouroux’s Hornera; but it is evident from Mr. Lonsdale’s 
observations that this was an erroneous collocation.’ The type—Tham- 
niscus dubius, Schlotheim—is very well described by King, and also well 
figured, but it was not possible, at the time he wrote, to clear up satisfac- 
torily all the points raised by him. In the text, and also in the figures 
(pl. V. fig. 10), Professor King indicates that Thamniscus simulates the 
oharacter of Synocladia ; this was clearly an error, as has been pointed out 
by Mr. G. W. Shrubsole in his paper on ‘ Thammniscus: Permian, Car- 
boniferous, and Silurian’ (‘ Quart. Journ. Geo. Soc.’ vol. xxxviii. p. 341). 
Of the other genus I may say that the typical Acanthocladia, King, and 
Ichthyorachis, M‘Coy, appear to cover the same ground ; but itis impossible 
to include in the genus species so different in their structural characters as 
Glauconome pluma, Phill., and G. bipinnata, Phill. I accept the dia- 
gnosis of Acanthocladia anceps, Schlot., and take it as the generic type. 
THAmniscus, King. 
Restricted by G. W. Shrubsole (op. cit. p. 343). 
Zoarium multiform. Branches free, round, frequently and regularly 
bifurcating; more or less in one plane. Zowcia on one side. Cells 
immersed, round, arranged in oblique lines. Reverse foraminated. 
Silurian Thamniscus crassa, Lonsdale = Hornera, Lonsd. 
a s delicatula, Vine = Hornera, ? Vine. 
Carbonif, 3 rankinet, Young & Young. 
a Ss carbonaria, Vine. 
Permian és dubius, King. 
? Foramina on the reverse in one species. 
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