6 PEOCEEDINGS OF THE NATIONAL MUSEUM vol.76 



but he figures it isolated from the mural rim and gives it 0.18 mm. in 

 width. It is difficult to apj^reciate these chitinous organs on the dry 

 specimens. Our specimens are poorly located on their substratum 

 and can be photographed only with difficulty. Nevertheless, in spite 

 of their imperfections, they show great micrometric variations. We 

 have measured Zs = 0.60-0.73 mm. and Zs = 0.50-0.45 mm. 



The figures of Jullien measure 0.80-0.64 mm. Waters for 31. 

 capriensis speaks of a length of 0.60-0.70 mm., and his figure indi- 

 cates 0.84—0.44 mm. The mural rim is isolated and finely granulated. 

 The small granulations are not always clearly visible; for this reason 

 we have introduced doubtfully Memhrani'pora capriensis Waters, 

 1898, which is figured with a smooth mural rim but in which the 

 ovicell is clearly endozooecial. 



The two small oral spines cited by Jullien are not visible on our 

 specimens. Smitt did not figure them, so they appear inconstant 

 and fragile. 



We have not discovered this species in the dredgings made by the 

 Albatross in the Gulf of Mexico, and we therefore can not confirm 

 the observations of Smitt. 



Our specimens from the Galapagos were dredged living on dead 

 Cellepores at 40 fathoms of depth. 



Biology. — " In the lowest state of development, it is a thin, glossy, 

 yellow-white shining crust. In the zooecia, covered by their thin, 

 translucent ectocyst, within the area, the bundle of tentacles and 

 the tnusculi retraetores operculi clearly present themselves through 

 their black color." (Smitt.) The ectocyst of the adult zooecia 

 easily loses its clearness. 



This species has been observed on corals, on dead bryozoa {Gelle- 

 pora^ Steganoporella., etc.), on Myfilus and on fragments of dead 

 shells. All the specimens collected to the present time appear to 

 have lived at the depths where they were dredged. These vary from 

 2 to 717 meters, which reveals a great facility of adaptation to bathy- 

 metric and thermometric conditions. However, this is an equatorial 

 or subequatorial species in which the extension toward the north 

 does not transgress beyond the Mediterranean. We are ignorant of 

 the causes which maintain it in these actual biologic limits. 



The species was in reproduction at the Cape Verde Islands on 

 July 27, 1883, but at the Galapagos Islands our specimens were 

 ovicelled on April 7 to 9, 1888. 



The simultaneous occurrence in the Gulf of Mexico and the 

 Galapagos Islands and in the Quaternary of Panama indicates the 

 ancient communication between the Pacific and the Atlantic and the 

 recent formation of the Isthmus of Panama. The species common 

 to these two oceans are now rather rare. At the Galapagos Islands 



