50 PEOCEEDINGS OF THE NATIONAL MUSEUM vol.76 



It is deprived of an oeciostome, and we do not still understand the 

 method of escape of the larvae. It may be necessary to create a spe- 

 cial genus, for in true Diaperoecia there is a fine submedian and 

 salient oeciostome. 



Occurrence. — Galapagos Islands, D. 2813, 



Gotypes.—C2it. No. 8526, U.S.N.M. 



DIAPEROECIA SUBPAPTRACEA, new species 



Plate 12, Figures 1-4 



Description. — The zooecium is discoidal, simple or composite, sur- 

 rounded by a very thick, wide, and porous margin. The tubes are 

 little distinct, with a short and very oblique peristomie; the peris- 

 tomes are thick, round, or oval, very close together, arranged in 

 quincunx on the young colonies but in radial very irregular rows on the 

 old zoaria. The ovicell is located on the zoarial margin; it is long, 

 convex, fusiform, perforated by tubes, often closed by a calcareous 

 lamella. 



Measurements. — Diameter of orifice, 0.08 mm.; diameter of peris- 

 tome, 0.11 mm. ; maximum diameter of colonies, 7.5 mm. 



Affi,nities. — This species is the perfect representation of Actinopora 

 papyracea D'Orbigny, 1852,^ from the Maastrichtian of Meudon near 

 Paris. If we can not make the comparison complete, it is because the 

 ovicell of the fossil is unknown. 



Biology. — ^When two colonies are coalescent they never cover each 

 other but arise from two different larvae. It is not rare, even in the 

 Cheilostomata to see many colonies on the same shell for they arise 

 from the same swarm of larvae which seem to travel together. 



It is most remarkable to note, as in Figure 1, larvae from an un- 

 known colony fix themselves on the same substratum at almost the 

 same place so that colonies are superposed. On our figures we can 

 note that the larvae arrived here for five years or seasons with an 

 almost mathematical precision. Moreover, in order that there be 

 superposition, it is necessary that the inferior zoarium be dead. Such 

 a small disk is born, grows, and dies the same year. We have here a 

 good example to evaluate the length of the zoarial life. This species 

 is not only interesting because of its archaic aspect but also it reveals 

 the voyage of the larvae in swarms and the duration of the zoarial 

 development. 



The ovicell belongs to the group of Diaperoecia without oeciostome. 



Occmrence. — Galapagos Islands, D. 2813. 



Gotypes.—Q^i. No. 8527, U.S.N.M. 



1 Bryoz. Cret., pi. 643, figs. 12-14. 



