137 
Retepora proper, the branches are sinuous and form meshes, and not regular 
rows of fenestrules. Its likeness to the genus Phyllopora, W. King, is 
still greater, as it differs essentially from it only by the fact that its cells 
cover the internal surface, while among the Phyllopora it is just the reverse; 
among these last, again, the cells are less closely packed, and more regularly 
arranged in lines. These two characteristics I consider sufficient to prove a 
different organization of the animals belonging to each group, and authorise 
a generic separation. Rrotoretepora is distinguished from Polypora, McCoy, 
and Synocladia, W. King, by the absence of cells on the cross-bars which join 
the various branches in the first, and by the small keels serving to bound and 
separate the rows of cells in the second. Again, the fenestrules of these last 
have a polygonal form, which makes them easy to recognise. 
Geological Distribution. — After having studied most of the forms 
which present some analogy to the species that I now propose to constitute a 
new generic group, and having carefully compared them, I am convinced 
that no species of this group is anterior to the Devonian, or posterior to the 
Carboniferous Period. The principal species, most of which have been 
described under the generic names of Fenestella, and Polypora, are as 
follows : — 
1. Protoretepora balaniana, A. cT Orhigny Ketepora retiformis, Miolie- 
lin, non <S'cA^o^Aeim^^^=Penestella antiqua, Lonsdale, non Gold-> 
fuss.^^'^ 
2. Protoretepora (Polypora) mexicana, H. A. ProutP^ 
3. 
?5 
(Polypora) Shumardii, LI. A. Prout.^^'> 
4. 
(Eenestella) ampla, Lonsdale.^^^ 
5. 
35 
(Polypora) Halliana, D. A. ProutP 
6. 
35 
(Polypora) hamiltoniana, H. A. ProutP''^ 
Of these six species, the first only is Devonian, and is found in the upper beds 
of that system ; the others are Carboniferous. So far none of these last have 
been met with in Europe. * (*) 
(') Prod. Pal., I, p. 100. 
O Mon. Zoopliyt., p. 190, pi. 49, fig. 7. 
P) Geol. Trans., Sec. Ser., Vol. V (2), and Phillips, Pal. Foss. Cornwall, p. 84, pi, 12, fig. 38. 
(*) Trans. Acad. Sc. St. Louis, I, pi. 16, fig. 2. 
(5) lUd., pi. 16, fig. 3. 
(•') Strzelecki, Phys. Descr. N. S. Wales and V. D. Land, p. 268, pi. 9, fig. 3. 
(’) Procs. Acad. Sc. St. Louis, I, p. 680, and Geol. Survey Illinois, II, p. 411, pi. 11, fig. 6. 
(») Ihid., II, p. 124, pi. 10, fig. 6. 
