102 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 56. 



The position of the attached form near the aperture suggests a 

 commensal condition. There is no fusion between the two, for the 

 attached form falls away, leaving a clean-cut surface. 



The degree of deviation from a symmetrical condition depends on 

 the length of time of attachment. In figure 4 the attached specimen 

 is on a large Cydammina which has reached nearly its full develop- 

 ment and the deviation is very slight. In smaller specimens like 

 figure 2, where several chambers have been added since the attached 

 species was in position, there is a marked deviation. In figure 3, 

 where specimens are attached to both sides, a sort of symmetry 

 results as both sides deviate from their normal line. 



IRIDIA CONVEXA, new species. 



Plate 25, figs. 1-4. 



Description. — Test attached, single chambered, lower surface con- 

 forming to the surface of attachment, upper surface strongly convex, 

 whole test slightly longer than wide; wall thin, ohitinous, with a 

 slight amount of arenaceous material either on the exterior or incor- 

 porated in the wall; apertm^e not evident; color yellowish-brown, 

 horny. Diameter, 0.50 to 0.65 mm. 



Type-specimen.— ({]. S.N. M. Cat. No. 10441a) horn Albatross D2213, 

 off the northeastern coast of the United States; latitude 39° 58' 30" 

 N. ; longitude 70° 30' W.; depth, 384 fathoms; bottom temperature, 

 39.5° F. At this station there are numerous specimens, all attached 

 to specimens of Cydammina cancellata H. B. Brady. 



I have placed this species under the genus Iridia erected by Heron- 

 Allen and Earland, although this species differs in some respects from 

 the type-species /. diaphana Heron-Allen and Earland. 



It is unusual among the foraminifera to find attached forms with 

 any definite relation of position as seems to occur in the case of these 

 two species, and although the idea of commensalism may not be 

 demonstrated here it is at least strongly suggested. 



EXPLANATION OF PLATE 25. 



Fig. 1. Cydammina cancellata, with two specimens of Iridia convexa attached to the 

 same side, a, side view ; 6, apertural view. 



2. Cydammina cancellata, with deep excavation iu the umbilical region due to 



attachment of Iridia convexa. a, side view, 6, apertural view. 



3. Cydammina cancellata, with specimens of Iridia convexa attached to the opposite 



sides. 



4. Adult specimens of Cydammina cancellata, with specimen of Iridia convexa 



attached near the aperture, a, side view; h, apertural view. 

 All figures multiplied by 25. 



