ART. 22. CYCLOSTOMATOUS BRYOZOA — CANTT AND BASSLEE. 103 



In longitudinal section the tubes are short, cylindrical, recurved at 

 their extremity. The gemmation is triparietal, the third wall being 

 that of a very thick basal lamella. The specimens being bilamellar, 

 this latter is often visible as a median lamella. The mesopores are 

 very short, expanded ; their walls and also those of the tubes in their 

 recurved portions are moniliform. 



In transverse sections the tubes are all equal and in consequence 

 cylindrical. There are no smaller tubes adjacent to the median 

 lamella, and the gemmation is therefore triparietal. The median 

 lamella is very thick, undulated or sinuous, rarely rectilinear. 



In meridian sections the tubes have the usual lozenge shape. 



The exterior aspect is quite variable. One characteristic of this 

 species is that unilamellar expansions often incrust the bilamellar 

 frond. Well preserved young specimens have a slightly salient, ob- 

 lique peristome, in this respect resembling Chilopora but the older 

 specimens strongly calcified lack the peristome. Certain fronds ex- 

 hibit large irregular spaces composed of mesopores alone. The 

 diameter of the orifices is 0.08 to 0.10 mm., and that of the mesopores, 

 0.02-0.04 mm. 



The J^oung fronds grow distally and laterally. Their transverse 

 section is traversed entirely by the median lamella. Other fronds 

 growing solely at their distal extremity have the median lamella com- 

 pletely surrounded by tubes. 



Occurrence. — Cretaceous (Maastrichtian) : Maastricht, Holland. 



Plesioty pes. —Cat. No. 68952, U.S.N.M. 



DITAXIA PARVIPORA. new species. 



Plate 17, figs. 1-8. 



1900. Ditaxia anomalopora Canu, Note pr61iminarie sur les Bryozoaires de 

 Tours, Comptes Reudus Association frangaise Avancement Science, 

 sess. 2, p. 409. 



Description. — The zoarium is free, bilamellar, formed of much com- 

 pressed, flabelliform, branching fronds. The tubes are short, cylin- 

 drical, without peristome, of small diameter, with triparietal gem- 

 mation, recurved at their extremity where the walls are thickened. 

 The mesopores are small, quite short, expanded, and as numerous as 

 the tubes. The ovicell is of medium size, smooth, convex, subround, 

 its contours indefined ; the oeciopore is very small and central. 



Measurements. — 



Diameter of tubes 0.08 mm. 



Width of fronds 3.00 to 5.00 mm. 



Sti^cture. — At the surface it is difficult to distinguish the tubes 



from the mesopores and the distinction is possible only on very well 



preserved specimens, but in tangential sections the tubes appear with 



a larger diameter. The much expanded form of the mesopores is the 



20107— 22— Proc. N. M. vol. Gl 38 



