GIRTY, ^^EW CARBONIFEROUS FOSSILS 207 



irregularly oval or slightly petaloid shape. Variable in size and outline, 

 usually from .18 to .21 mm. in longest diameter, rarely .28 mm. Irregularly 

 arranged, rarely in contact, more often with one or even two rows of meso- 

 pores intervening. Mesopores irregular in size and arrangement. The largest 

 are of about half the diameter of the zocecia, but it is rare to find them so 

 large. They are subangular and of regular shape, usually separating the 

 zooecia in a single row, less often two rows, rarely three. Six or less of the 

 zocecia occur in a linear distance of 2 mm. There are rare maculae consisting 

 of mesopores or small cells. Acanthopores are of two sizes. One kind is 

 very large and very rare, developed in the walls of the zooecia, which they in- 

 dent. The other is much smaller, developed as rows of granules along the 

 middle of the walls of the zooecia, occasionally in the mesopore walls. Both 

 kinds are, however, scantily developed and considerable areas occur in which 

 no acanthopores can be seen at all. 



When the cells are cut lengthwise, they are seen to be slightly oblique, very 

 rapidly expanding, with a short prostrate portion, perhaps strictly vertical 

 only in the mature region, which is quite narorw (.14 to .28 mm.). The 

 cortical zone is abruptly and greatly thickened, the mesopores being confined 

 to it, so that the zooecia are much larger below than near the surface. Tabula?, 

 so far as observed, are entirely lacking both in the zooecia and the mesopores. 



Polypora mesleriana sp. nov. 



Zoarium apparently rather small for the genus, very irregular in growth, 

 with the surface contorted and the branches often strongly bent. Owing to 

 this irregularity, the measurements and relations vary greatly. There are 

 5' branches and 4 rows of fenestrules in 5 mm., but 4 branches and 3 rows 

 may occur on the same specimen. The branches are relatively slender when 

 first introduced and about twice as broad before division, to which circum- 

 stance and the fact that they sometimes diverge rapidly the difference in 

 measurement noted above may be ascribed. Longitudinally, from 2 to 2.5 or 

 even 3 fenestrules occur in 5 mm. They are usually elongate, nearly twice as 

 long as they are wide and subrectangular to subelliptical in shape, but they 

 vary considerably in proportion. The branches range from one half to nearly 

 twice the fenestrules in width in extreme cases, but the average is inter- 

 mediate. They are rounded when narrow and flattened when broad and are 

 very much broader than the dissepiments which are slender (on the reverse) 

 and somewhat depressed. On this side, the branches are marked by fine but 

 sharp and regular longitudinal strire, which, in some instances, swing off onto 

 the dissepiments. Over the older portions, these markings appear to be lost, 

 but they are apt to show when exfoliated, indicating that they are structural 

 as well as superficial. There is some evidence that they are marked by fine 

 granules or spines. 



On the obverse, tne apertures usually occur in 4 rows (more rarely 3 or 5). 

 They are situated in grooves, which lie between rather strong ridges. The 

 crests of the latter seem to have a zigzag course and bear strong spinules 

 which have a regular arrangement alternating with the aperture. Of the 

 latter, 5 to 7 occur opposite a fenestrule. They are oval in shape with sharply 

 elevated peristomes and appear to be covered in some cases at least with 

 centrally perforated opercula. 



