198 Trof. H. A. Nicholson — New Devonian Fossils. 



of two lines ; dissepiments exceedingly narrow, not more than one- 

 hundredth of an inch in width, slightly expanded at their points 

 of junction with the branches, quite straight, and separated from 

 one another by intervals of one line, sub-alternate in contiguous 

 rows. No cells upon the dissepiments. Fenestrules oblong, 

 regularly rectangular, nearly twice as long as wide (nearly one 

 line in length and less than half a line in width) ; three fenestrules 

 in a quarter of an inch measured vertically, and five in the same 

 space measured transversely. Two marginal rows of large flask- 

 shaped cells, between which are two or sometimes three rows of 

 minute elongated cells, which probably occupied a central keel. 

 Four of the large marginal cells to the length of a fenestrule, 

 and one opposite the origin of each dissepiment. 



As in the case of the preceding species, I have only a single ex- 

 ample of this species ; but its characters are so peculiar that I have 

 no doubt as to its specific distinctness. Our specimen is one ex- 

 hibiting the back of the polyzoary, but the outer striated non- 

 celluliferous layer has been denuded, and the proximal ends of the 

 cells are thus brought into view. (Fig. 23.) 



In its general form, F. marginalis is clearly a genuine Fenestella, 

 as shown by the straight branches, the distinct straight non-cellu- 

 liferouB dissepiments, the rectangular fenestrules, and its possession 

 of a row of large cells on each side of each branch. This last charac- 

 ter separates it from Polypora, and the others distinguish it from 

 Betepora. The specimen does not enable me to affirm with certainty 

 that the two marginal rows of cells were separated by a median 

 keel ; but it appears highly probable that this was the case. In 

 the genus, or sub-genus, Fenestrellina, D'Orbigny, the mesial keel, 

 separating the two rows of large lateral cells, carries a central row 

 of minute cells. In F. marginalis, however, the space between the 

 lateral rows of cells carries a series of minute crowded cells, which 

 are arranged in two or sometimes in three alternating rows ; so that 

 the central keel, if present, must have exhibited the openings of two 

 or three rows of cells. This character, so far as I am aware, has 

 not hitherto been noticed in any species of Fenestella, except F. 

 rigidiila, McCoy, and it may, perhaps, afford a ground of sub-generic 

 distinction. 



In its general form, F. marginalis exhibits some resemblance to 

 F, magnijica, but its dimensions are much smaller. It possesses four 

 branches in a space of two lines, and five fenestrules in three lines 

 measured transversely, whilst the dissepiments are exceedingly thin, 

 and the length of the fenestrules is nearly double the width. In the 

 latter species, on the other hand, there are three branches in a space 

 of two lines, and about three fenestrules in three lines measured 

 transversely or diagonally, whilst the dissepiments are about as 

 thick as the branches, and the fenestrules are only slightly longer 

 than wide. 



Locality and Formation. — Corniferous Limestone, Port Colborne. 



