108 
tical septum, traversing the short diameter of the frond, and prolonged on either side into a 
keel. Leaving this point, however, out of the question, as uncertain, there remain the fol- 
lowing differences :—1. In Ptilodictya the cells are not furnished with prominent mouths, 
but with depressed apertures, and these are arranged in rows, which are separated by distinct 
thread-like elevated lines or striw. On the other*hand, the cells of Zwniopora have pro- 
minent pustuliform openings, and they are usually not separated by any lines or ridges of 
any kind. In some examples from the Hamilton group 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 remain- 
ing rows of cells not marked off in this way. 2. There is no mesial keel or elevated ridge in 
Ptilodictya, separating the ccencecium into two symmetrical lateral halves. On the other 
hand, the most conspicuous feature in 7eniopora is a strong elevated longitudinal carina on 
either side of which the cells are arranged in alternating lines. 3. Whilst some examples of 
Teniopora show a distinct non cellulifgrous marginal zone on either side, as exists in Ptilodictya, 
others do not appear to possess any such structure; and in any case this zone appears, when 
present, to be smooth and not striated. Upon the whole, therefore, whilst recognizing the 
general affinities of Teniopora to Ptilodictya, I think the former may safely be regarded as a 
distinct genus. 
The following two species of Tniopora have come under my notice as occurring in the 
Hamilton group ; but asall my specimens are fragmentary, there are several important points 
connected with their structure, which I have found myself unable to elucidate. I have also 
specimens from the same formation in the State of New York, some of which appear to be 
identical with one of our Canadian species, whilst others present certain differences which may 
perhaps be of specific value. 
132. TaNr1oporA EXIGUA (Nicholson). 
Teniopora eaigua (Nicholson), Geological Magazine, March, 1874. 
Polyzoary forming flattened linear 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, until the sharp-edged lateral margins are 
reached. Both sides of the ccencecium carry a well marked longitudinal ridge or keel, 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 im- 
mersed in the substance of the ccencecium, 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 dia- 
meter of the cell-mouths themselves. The cells extend on either side of the midrib, quite to 
the edge of the coencecium, and there appears to be no marginal non-celluliferous zone. 
From the following spe- 
cies, Teniopora exigua is 
distinguished by its much 
smaller width, its more fre- 
quent division, its much 
less strongly elevated me- 
sial keel, and the apparent 
absence of any distinct non- 
celluliferous marginal area. 
One specimen exhibits at 
the base a small conical 
expansion from which the 
Teniopora exigua (Nich). a. Portion of a frond, natural size ; b. The same enlarged, branches proceed distally, 
the portion drawn in outline being conjectural; c. Portion of the same still furtheren- and which terminates prox- 
larged. From the Hamilton group. imally Haig singular, and 
clearly natural, circular perforation of about one-fourth of a line in diameter, There are 
also indications in this specimen (fig. 470.) that the branches of the frond were bilaterally or 
Fig. 47. 
* 
