122 Frof. H. A. Nicholson — New Devonian Fossils. 



specimens lead me to believe that it is absent, and that there is 

 instead a vertical septum traversing the short diameter of the frond, 

 and prolonged on either face into a keel. Leaving this point, how- 

 ever, out of the question, as uncertain, there remain the following 

 differences : 1. In Ptilodictya the cells are not furnished with promi- 

 nent mouths, but with depressed apertures, and these are arranged in 

 rows which are separated by distinct thread-like elevated lines or 

 strias. On the other hand, the cells of Teeniopora have prominent 

 pustuliform mouths, and they are usually not separated by any lines 

 or ridges of any kind. In some examples from the Hamilton Shales 

 of the State of New York, the first row of cells on either side of the 

 keel has a limiting thread-like line ; but I cannot detect any such 

 structure in our Canadian specimens, and even the former have the 

 remaining rows of cells not marked off in this way. 2. There is no 

 mesial keel or elevated ridge in Ptilodictya, by which the coencecium 

 is separated into two symmetrical lateral halves. On the other hand, 

 one of the most conspicuous features about T<sniopora is a strong 

 elevated keel on each aspect of the frond, on either side of which 

 the cells are arranged in alternating lines. 3. While some species of 

 Tceniopora show a distinct non-celluliferous marginal zone, such as 

 exists in Ptilodictya, others show no such character, and in any case, 

 even when present, this zone is smooth and not striated. Upon the 

 whole, therefore, whilst recognizing the general affinities of Tanto- 

 pora to Ptilodictya, I think the former may safely be regarded as a 

 distinct genus. The following two species of Tmiiopora have come 

 under my notice from the Hamilton Formation of Canada. 



T^NiopoKA EXiGUA, Nicholson. PI. VI. Fig. 13. 



Polyzoary forming linear flattened expansions, which branch 

 dichotomously at angles of about 60°, and at intervals of from 

 one and a half to three lines. The width of the frond is about 

 a line or a little over, and its thickness in the centre is about one- 

 third of a line, from which point it rapidly diminishes in thickness 

 till the sharp-edged lateral margins are reached. Both sides of the 

 coencecium carry a well-marked longitudinal carina, which occupies 

 a mesial position, and on either side of which are three or four 

 longitudinal rows of cells. The cells are alternately disposed in 

 contiguous rows, so as to form a series of short transverse obliquely- 

 ascending lines consisting each of three or four cells. The cells are 

 immersed in the substance of the coenoecium, and their mouths are 

 circular and prominently elevated above the general surface. About 

 six cells occupy the space of one line, measured longitudinally, and 

 the intervals between them are equal to, or slightly greater than, 

 the diameter of the cell-mouths themselves. The cells extend on 

 either side of the midrib quite to the edge of the coenoecium, and 

 there appears to be no non-celluliferous marginal zone. 



From the following species, Tceniopora exigua is distinguished by 

 its much smaller width, its more frequent division, its much less 

 Strongly elevated midrib, and the apparent absence of any distinct 

 marginal non -poriferous area. 



One specimen (Fig. 13, a, b) exhibits at the base a small conical 



