770 
BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 
Measurements . — 
Distance between the fascicles. 
Width of the fascicles 
Diameter of the peristomes 
Maximum zoarial width 
0.17 mm. 
0.11 mm. 
0.12 mm. 
1.8 mm. 
Affinities. — This species much resembles Retecava , in the arrangement of its 
pores, but differs in the nature of its ovicell, which is entirely frontal and not 
located on a single side of the zoarium. 
The knowledge of the nature of the pores and of better ovieells will perhaps 
permit of the discovery some day of the true position of this species. 
This species differs from Idmonea subcancellata Manzoni, 1877. in its fascicles, 
which are much more salient and formed of more than three to four tubes. 
Occurrence. — Lower Jacksonian: Three and one-half miles southeast of Shell 
Bluff post office, Georgia (rare.) 
Cotypes. — Cat. No. 65341, U.S.N.M. 
Genus IDMONEA Lamouroux, 1821. 
1821. Idmonea Lamouroux, Exposition Methodique des Polypiers, p. 80. 
The ovicell is irregular, little lobed or not at all, subsymmetrical, placed on 
the median crest of the zoarium. The fascicles are not entirely enveloped by the 
ovicell. The oeciostome is excentric, nonterminal, and replaces the first or the 
second tube of a fascicle. The basal lamella is simple and bears no pores. 
Accepted genotype. — Idmonea atlantica Johnson. 1847. 
Range. — Senonian-Recent. 
This genus differs from Tubulipora Lamarck, 1816, in the absence of well- 
developed lobes, and in its oeciostome nonsubcentral, and occupying a fixed place 
among the fascicles. 
Historical. — The genus Idmonea was founded by Lamouroux upon I. triquetra , 
an incrusting form found in the Bathonian at Banville, France. The history of 
the genus has been given many times, but the greatest confusion has existed among 
paleontologists as to its interpretation. Among the zoologists, however, the name 
Idmonea has always been applied to the well-known zoarial form bearing an 
anterior ovicell. Former authors were ignorant of the importance of the ovicell 
and even of its existence. All speculation on their work is absolutely useless and 
idle. Usage and the principle of least change seems to us the only considerations 
to be regarded, and we have therefore followed the zoologist in regarding Idmonea 
atlantica Johnston, 1847, as the accepted genotype. 
Determination. — The determination of species of Idmonea is very difficult in 
spite of the introduction, due to Pergens, of the micrometric dimensions; this is 
in reality because we have only isolated fragments for study. If the ovicell in 
rapport with the number of larvae and the fissiparity of the primary embryo is 
quite variable in form and position, the oeciostome is more constant, for it is only 
in rapport with the form and size of the larvae. But the larvae of the different 
families of Cyclostomata are much alike. It is necessary, therefore, to seek another 
