HEMITRYPA. 177 



ments very short, similar in width to the branches, but lower and flatter. Cells 

 more or less regularly alternating in three or four rows, about eight or nine to 

 the length of the fenestrule, with circular and apparently slightly elevated 

 mouths. 



Size of a fragment, 12 mm. by 14 mm. 



Locality. — Lummaton. One or two specimens in my Collection, and two 

 doubtful specimens in the British Museum. 



Remarks. — Several of my specimens seem to group themselves together in 

 presenting rather a different macroscopic appearance from the preceding species, 

 but in only one of these have I been able to find traces of the cell-structure, while 

 the other characters are too indefinite to found any distinction upon them. Even 

 in the case of the last-named specimen it may be questioned how far its features 

 may be due to its state of preservation. Still it certainly does bear a very 

 different appearance, and it may perhaps be separated by the following characters : 

 — the upper part of the cells are much less free, the mouths simply rising in a kind 

 of crater from the branch, the number of the rows of cells seem to be decidedly 

 fewer, the branches are more undulating, and the network is generally, though not 

 always, a good deal smaller. 



Affinities. — None of the numerous American forms described by Ulrich seem 

 to bear much resemblance to this species, the nearest being P. submarginata, 

 Meek, 1 which has more numerous ranges of cells, and P. gracilis, Prout, 2 which 

 has very long lanceolate fenestrules. 



3. Genus. — Hemitrypa, Phillips, 1841. 



Zoarium rigid, undulating, or infundibuliform. Apertures of the zocecia in two 

 ranges separated by a keel, which at regular intervals is elevated into small 

 pillars bearing a superstructure or guard. Guard lying parallel to the celluliferous 

 frond, and forming a regular network with small round or hexagonal openings, 

 corresponding in number and position to the zocecial apertures beneath them, and 

 constituted by straight or zigzag bars, one series corresponding to the branches 

 and supported by the carinal pillars, and a second series, usually somewhat 

 thinner, suspended midway between and united to the former by similarly placed 

 transverse processes. (Silurian to Carboniferous.) 



1 1871, Meek, ' Pal. Eastern Nebr.,' p. 154, pi. vii, figs. 7 a, b; and Ulrich, 'Geol. Surv. Illin.,' 

 vol. viii, p. 602, pi. lxi, figs. 6 — 6 b. 



2 1860, Prout, 'Trans. St. Louis Acad. Sci.,' vol. i, p. 580; and 1890, Ulrich, 'Geol. Surv. 

 Illinois,' vol. viii, p. 590, pi. lxi, figs. 10, 10 a. 



23 



