94 BULLETIN 106, UNITED STATE.- NATIONAL, MUSEUM. 



nnd d'tfinittrx. Like (''<//<>/>< H/H l<nnt I/OXHM, this species presents on 

 its zoarial surface subcolonies which do not originate from a larva, but instead 

 from the especial proliferation of a subjacent zooecium (fig. 12). These develop 

 chiefly at the bifurcations of the algae, which are the parts most constant and least 

 susceptible to growth which might disorganize the zoarium. In tangential thin 

 sections the interopesial cavities have special walls (fig. 1C). On the inner face of 

 the zoarium the zooecia are elliptical and provided with a distal collar (fig. 1-1). 



The mural rims are adjacent, but may be sometimes separated by a very small 

 furrow. The marginal zooecia are deformed wherever the snbcolonies meet. On 

 certain zoaria there are some zooecia bearing a kind of gymnocyst rather well devel- 

 oped; again the interopesial cavities sometimes have the form of prominent and 

 pointed avicularia. 



This is a good-sized fossil, and its large zoarial dimensions will aid in its 

 determination even in the field. 



Conopcum arborescent differs from (.'. l<uft<llvxiirn in the form of its zoarium, 

 in the oval shape of the opesium, in the rarity of furrows separating the zooecia. 

 and in the greater thickness of the mural rim. 



<>i ci/r/'f/ifi . Lower Jacksonian (Moody:- marl): Jackson. Mississippi (com- 

 mon) ; 2 miles north of Robert, Mississippi (common). 



Cotypes.C&t. No: 63873, U.S.X.M. 



Genus HELIODO.MA Calvet, 1907. 



1907. Hcliiiilniiiii CAT.VKT, Br.voznaires Expedition Scientilique flu Tntrnilleur et dn Tulix- 

 iiiini, p. 396. 



The zooecia, with frontal provided with a membraneous area, are arranged 

 following two concentric spiral series in which they alternate, separated by a spiral 

 series of vibracula (Calvet). 



Genotype. PleHodoiini !/n/>/!r,/f,,, Calvet. 10<i7. Eecent. 



The two genera Cupuladria and lli'linilninii differ only in the place of the 

 vibracula. They can be maintained only if it is proved that the function of the 

 vibraculum is different in them. The name of UiVimlnnni would then have the 

 right of priority. 



Genus MEMBRANIPORINA Levinsen, 1909. 



1909. Mciiibrriiiiiiorhiii LEVIXSEX, Morpliuln-ir;!] mid Systematic Studies on the Cheilostoma- 

 tous Br.vo7.oa, p. 145. 



Membranipores exhibiting neither ovicells nor avicularia. 



Membramporina is not a true ge.nus. but is simply an artificial grouping pro- 

 posed by Levinsen for the reception of species incompletely described or of which 

 we have insufficient information to place them more definitely. 



MEMBRANIPORINA RIMULATA Ulrich. 1901. 

 I'lati- 1. h::s. 1. :.'. 



1'inl. Mi iii/n-tiiiiiHirti riiiiiilntii T'I.KK H. .Maryland Kenlinjiciil Survey, Eocene, p. 211, i>l. <". 

 fiprs. 1, 2. 



,-;,/;, nil description. "Zoarium adnate. forming a thin, single sheet of 

 indefinite extent. Zooecia hexagonal in form, arranged quincuncially, with the Ion- 



