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PROCEEDINGS OF THE NATIONAL MUSEUM 



VOL. 72 



is then quite natural. We note, in fact, no essential difference between 

 the two species. However, Semihaswellia sinuosa differs from H- 

 prohoscidea in its articulated zoarium (and not branched) and in its 

 lateral, not distal ovicell. 



Among the fossils from the Jacksonian we have found a smaller 

 species, Semihaswellia exilis Canu and Bassler, 1920, in which we have 

 been able to explain the structure. The anologies with the present 

 species are evident and permit us to deduce from it that the large 

 hollow apophysis is in reahty a base of articulation and that the 

 colony was articulated as a base of the figured segment proves. (Fig. 

 22, pi. 66.) 



As all these species are quite rare and their study is quite incom- 

 plete, the task of the paleontologist is very difficult. Semihaswellia 

 prohoscidea Waters, 1889, has been found in the pteropod ooze at 729 

 meters of depth. 



Occurrence. — Albatross Station D. 2392, Gulf of Mexico; 28° 47' 

 30"N.; 87°27'00"W.; 724fms.; brown gray mud. 



Cotypes.—Csit. No. 7591, U.S.N.M. 



Genus TESSARADOMA Norman, 1868 



TESSARADOMA GRACILE Sars, 1863 



Plate 15, Figure 5; Plate 28, Figure 6 



1873. Tessaradoma boreale Smitt, Floridan Bryozoa. Kongl. Svenska Veten- 



skaps-Akademiens Handlingar, vol. 11, p. 32, pi. 6, figs 143-145. 

 1903. Tessaradoma gracile Jullibn, Bryozoaires de VHirondelle. Resultats 



des Campagnes scientifiques du Prince de Monaca, p. 74, pi. 3, fig. 4, 



and pi. 14, fig. 2. (Bibliography,) 

 1907. Tessaradoma borealis Calvet, Bryozoaires. Expedition Scientifique 



Travailleur et Talisman, p. 405. 

 1912. Tessaradoma gracile Nobdgaard, Revision av universitetsmusets 



samling av norske Bryozoer. Kgl. norske Videnskaber Selskabs, 



Skriften, p. 20. 

 1918. Tessaradoma gracile Nordgaard, Bryozoa from the Arctic region. 



Tromso Museums Aarshefter, vol. 40, p. 53 (numerous localities cited, 



temperature) . 



It is difficult to recognize the true micrometric characteristics of 

 this species. The measurements taken from the figures of the authors 

 are extraordinarily divergent as may be noted from the following 

 examples: 





Canu col- 

 lection 



(North 

 Atlantic) 



Smitt, 1867 



Smitt, 

 1873 



Hincks, 1880 



Jullien, 

 1903 



D 2117 





Fig. 5 



Fig. 4 





Diameter of peristome 



Length 



Milli- 

 meters 

 0.16 

 .90 

 .60 



Milli- 

 meters 

 0. 18-0. 20 

 1.20 

 .60 



Milli- 

 meters 

 0.18 

 1.28 

 .60 



Milli- 

 meters 

 0.14 

 .70 

 .33 



Milli- 

 meters 

 0.10 

 .40 

 .24 



Milli- 

 meters 

 0.10 

 .40 

 .22 



Milli- 

 meters 



0.25 

 1 50-1 60 



Width 



75- 90 







