476 Notices of Memoirs — G. R. Vine on Fossil Polijzoa. 



their long axes corresponding with that of the branches, six or seven 

 in the space of one line measured longitudinally." " This Nicholson 

 considers to closely resemble P. fragilis, Billings, and it is possible 

 that it may be only a variety of Billings' species." ^ 3. P. flngellnm, 

 Nich. This also resembles P. gladiola, Billings, and it also very 

 closely resembles the P. Lonsdalii of our own Wenlock shale, 

 excepting that the " attenuated base " of our own species is rarely 

 "flexuous," but more often truncated and round. 4. P. fenestelli- 

 formis, Nich. All these species are typical, having the non-poriferous 

 margins and the central laminar axis. One species — Ptilodichja ? 

 arctiopora, Nich. — has affinities with P. raripora, Hall ; but Nicholson 

 doubts the possibility' of keeping these two species with the genus. 

 The cells closely resemble some of the characters of our own Silurian 

 species, but as there is evidently a departure from the original 

 types, it may be as well to study these passage forms, if such they 

 be, more carefully than they have yet been done. 5. P. coscini- 

 formis,'^ Nich. : Hamilton formation, Bosanquet, Ontario. 



For sjDecies allied to Ptilodicfya, Nicholson has founded two new 

 genera, and adopted one from Hall. 



1874. Tceniopora, Nicholson, Geol. Mag. 1874. 

 Clathropora, Hall, ,, ,, ,, 



1875. Heterodictya, Nicholson ,, ,, ,, 



In Tceniopora we have a zoarium that is a flattened, linear, cal- 

 careous expansion, with cells on both sides, the branches of which 

 are dichotomous. There is a median ridge on each face of the 

 zoarium, having a longitudinal direction, on the lateral halves of 

 which the cells are developed. These are longitudinally placed in 

 rows of from three to five. The margins are usually plain and 

 non-celluliferous. Two species are described : T. exigiia, Nich., and 

 T. penniformis, Nich., both from the Hamilton group. 



In Clathropora the zoarium is a kind of membranous flattened 

 expansion, with rounded or oval fenestrse of considerable size. The 

 cells are on both sides, separated by a thin laminar axis. The 

 fenestrse are surrounded by a striped non-celluliferous margin. One 

 species is described — C. intertexta, Nich. — from the Corniferous 

 Limestone, but in some respects it resembles P. cosciniformis, Nich., 

 of which mention has already been made. 



In Heterodictya the zoarium forms a simple, flattened, unbranched, 

 two-edged frond, with sub-parallel sides. The cells are in two 

 series ; the central cells are perpendicular to the base, the lateral 

 cells are oblique. " In the only species known — H. gigantea, Nich. 

 — the cells of a few of the median rows of the frond are straight 

 .... and, as I am only acquainted with an exceedingly large 

 species, I should, however, suspect that Flustra (Ptilodiciya) lanceo- 

 lata, Goldf., will very probably turn out to be an example of this 

 genus." ^ 



The material for a thorough revision of this genus is not easily 

 accessible. Many of the Bala series are beautiful casts only, and the 

 Upper Silurian species are often bedded in blocks of the Dudley 



1 md. p. 179. 2 Nicholson, Geol. Mag. Jan. 1875. ^ jfy.ia. 



