780 BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 



Affinities. Our fossil specimens have the aspect of the figures by Smitt, 1866; 

 Hincks, 1880; Manzoni, 1877; and Busk, 1875. However, the micrometric meas- 

 urements are generally smaller, although they are, on the contrary, essentially the 

 same as those of specimens dredged in the Mediterranean. 



In general aspect our specimens are quite different from the figures by Os- 

 burn, 1914, and Harmer, 1916, but the micrometric dimensions are closer. 



In 1909, Canu, deceived by an excellent figure by Milne -Edwards, 1838, identi- 

 fied Idmonea atlantica with Idmonea coronopm Defrance, 1821. He is not now so 

 sure, for he has been unable to find in the museum Milne-Edwards's type and the 

 micrometric measurements of the French specimens (interfascicular distance^ 

 0.30-0.40 mm.) are still less than those of our American specimens. 



This species differs from Tervia tumid a Smitt, 1871, in an interfascicular distance 

 somewhat smaller and in its fascicles which are much more protruding beyond the 

 zoarium. 



The difference from Idmonea grallator in the absence of the radicells is quite 

 difficult to note at sight. It can be made out only under the microscope, the interfas- 

 circular distance being always greater than 0.40 mm. 



Occurrence. Middle Jacksonian : Wilmington. North Carolina (very com- 

 mon) ; one-half mile southeast of Georgia Kaolin Co. mine. Twiggs County, 

 Georgia (rare); 12 miles southeast of Marshallville, Georgia (rare). 



Upper Jacksonian (Ocala limestone) : Chipola Elver, east of Marianna, Jack- 

 son County, Florida. 



Vicksburgian (Marianna limestone) : One mile north of Monroeville, Alabama 

 (rare). 



Plestotypes.C&t. No. 65353, U.S.N.M. 



IDMONEA PARVULA, new species. 



Plate 138, figs. 21-23. 



Description. The zoarium is free, very small, linear, bifurcated with triangu- 

 lar transverse section. The fascicles are little salient, much scattered, arranged 

 alternately on each side of the median crest, extending very little over the zoarial 

 margins; they are formed of two or three small, equal zooecia. The tubes are 

 small, visible, convex. The dorsal lamella is very convex, smooth. 



-Diameter of the tubes 0.06 mm. 



Distance between the fascicles 0.500.60 mm. 



Width of the fascicles 0.10 mm. 



Width of the zoarium 0.36 mm. 



Affinities. This is the smallest of our American species. It resembles some- 

 what Idmonea. filiformis in the narrowness of the zoarium : but it differs from it 

 in the frequent bifurcation of the zoarium and in a lesser interfascicular distance 

 (0.50 and not 0.90 mm.). 



Occurrence. Middle Jacksonian: Eighteen miles west of Wrightsville. 

 Johnston County, Georgia (rare). 



Holotype.Cal. No. 65417, U.S.N.M. 



Measurements. 



