PENNIRETIPORA. 191 



marks, e. g. the regularity with which the branches start from the centre of every 

 second cell on the midrib, their angle and length, and the serpentine general form. 

 The divarication of the main stem itself is rare, and I have not observed any 

 specimen in which it occurs more than once. The angle thus formed is curvilinear, 

 and is generally much less than that of the secondary branches; while the new 

 midrib immediately bears similar lateral branches, though probably at first they 

 are not so long as those on the old. The secondary branches alternate with each 

 other, though they sometimes seem nearly level. The dimensions seem to vary a 

 good deal in different specimens. 



Affinities. — Glauconeme pluma, Phillips, sp., 1 appears from the figures to have 

 longer and slighter branches, and more cells on the midrib between them. 



In G. pulcherrima, M'Coy, 2 the habit seems very different, the cell-mouths more 

 central, and the lateral branches " regularly attenuate." In G. gracilis, M'Coy, 3 the 

 cell-mouths are much larger and nodulate the sides, and the branches are much 

 broader than the intervals, but in some respects it bears much likeness to our 

 species. None of the American species described by Ulrich in the eighth volume 

 of the ' Geol. Surv. Illinois ' at all resemble it. 



G. stellipora, Young and Young, 4 is much more irregular, and has stellate cell- 

 mouths ; nor do any of the other species described by those authors 5 appear to 

 approach the present form. 



2. Penniretipora vikgata, n. sp. Plate XXIlI, figs. 9, 9 a. 



Description. — Zoarium small (?), slight, loosely ramose, consisting of a midrib, 

 from which occasional lateral branches start at an angle of about 50°, which in 

 their turn appear to bear similar and similarly set minor branches. Midrib slight, 

 about '25 mm. wide, straight, slightly tapering. Reverse face rounded, smooth or 

 minutely striated (?). Poriferous face sharply keeled, obliquely flattened on the 

 sides. Cells in two rows, triangular in longitudinal section. Lateral branches 

 few, unequally distant, slight, sometimes about 4 mm. long, with central keel and 

 two rows of cells, and apparently tapering to a subacute point. Numerous 

 (from five to ten ?) cells on the midrib in the intervals between the lateral branches. 

 Intervals unequal, and frequently about 2 mm. in length. 



Size. — A specimen (which is probably a fragment) measures 6 mm. long. 



1 1836, Phillips, ' Geol. Torks.,' vol. ii, p. 199, pi. i, figs. 13—15. 



2 1844, M'Coy, ' Synops. Carl). Toss. Irel.,' p. 199, pi. xxviii, fig. 4. 



3 Ibid., p. 199, pi. xxviii, fig. 5. 



4 1874, Young and Young, ' Quart. Journ. Geol. Soc.,' vol. xxx, p. 682, pi. xl, figs. 5 — 11. 



5 1876, Iidem, ' Proc. Nat. Hist. Soc. Glasgow,' vol. ii, pt. 2, p. 325; and 1879 ? vol. iv, p. 354. 



