ART. 22. CYCLOSXOMATOUS BRYOZOA — CANU AND BASSLER. 121 



curved at right angles and their walls are thicker. The mesopores 

 are regular ; that is to sa}^, somewhat parallel to the extremity of the 

 tubes; between two peristomes there are generally two, a large and a 

 small one, but the variations and exceptions are fjuite frequent. They 

 are always formed by ramifications of the proximal tube. 



In tangential section the tubes and the mesopores have thick walls. 

 Above each orifice there are always at least two mesopores arranged 

 somewhat transversally and not longitudinally ; this arrangement ex- 

 plains the presence of a small and a large mesopore in the longi- 

 tudinal sections. 



The presence of the median basal lamella gives to the zoarium the 

 aspect of a Mesenteripora provided with mesopores. The fronds are 

 rarely cylindrical, but are almost always slightly compressed. The 

 meridian section prepared in the immediate vicinity of the basal 

 lamella shows the losenge-shaped areas wider and less geometrical 

 than in the species with club-shaped tubes. They are longer when 

 the section is further removed from the basal lamella. 



Affinities. — The three species of Hagenow, Ileteropora tenera^ di- 

 chotoma^ and undulata, really form only a single species. Not only 

 are the sections absolutely identical, but all the intermediate stages 

 between these three forms have been found. Gregory, 1909, under 

 the name of /Sparsicavea vndulata, described a species with conical 

 tubes, without basal lamella, which we can not believe is the same as 

 Hagenow's species. 



The exterior aspect of these fossils is quite deceiving. For ex- 

 ample, Tretocycloecia dichotoma Reuss, 1847, has really an analo- 

 gous aspect, but nevertheless it is not provided with a basal lamella 

 and belongs to a different family. Likewise, the undulated aspect of 

 the zoarium is a character without importance, as may be observed 

 on a large number of species of different families. The section of 

 Hennig, 1894, is incomplete and we are not entirely certain of its de- 

 termination, since he has not figured the basal lamella. Likewise 

 Pergens, 1889, did not mention it in MuUlcrescis laxata D'Orbi"-ny 

 1854. \ ' ' 



Occurrence.— CvQi2iQQous (Maastrichtian) : Maastricht. Holland. 



Plesiotypes.—C?ii. No. 68965, U.S.N.M. 



GRAMMASCOSOECIA POROSA, new speciea. 



Plate 21, figs. 9, 10. 



Description. — The zoarium is branched or reticulated; the fronds 

 are divergent, irregular, and compressed (elliptical in transverse sec- 

 tion). The tubes are cylindrical, short, without peristome, with dor- 

 sal gemmation on the basal lamella. The orifices are arrano-ed in 

 irregular quincunx and more or less grouped around the porous ellip- 



