140 PEOCEEDINGS OF THE NATIONAL MUSEUM vol.72 



We have always trouble in understanding the selective faculty of 

 the larvae; the latter can not really choose their substratum of fixa- 

 tion; what is then the biochemical reaction which allows them to 

 subsist only on shells of gastropods? 



Occurrence. — Albatross Station D. 2363, east of Yucatan; 22° 07' 

 30" N.; 87° 06' 00" W.; 21 fms.; wh. r. coral. 

 Elbow Reef, Fla., 39 meters (Smitt) . 

 Tertiary, Miocene: Wilmington, N. C, and Mul- 

 drows Mills, S. C. Pliocene: Waccamaw River, 

 S. C. 

 Plesiotypes.— Cut. No. 7515, U.S.N.M. 



HIPPOFORIDRA CALCAREA Smitt, 1873 



Plate 22, Figures 5, 6; text Figure 30 



1873. Lepralia calcarea Smitt, Floridan Bryozoa. Kongl. Svenska Veten- 

 skaps Akademiens Handlingar, vol. 11, p. 63, pi. 11, figs. 220-223. 

 1914. Lepralia edax Osbukn, Bryozoa of the Tortugas Islands. Publication 

 Carnegie Institution, No. 182, p. 212. 



Structure. — The apertural width is from 0.08 to 0.09 mm.; there is 

 no umbo on the frontal in agreement with Smitt 's figure. The 



zoarial avicularia are very small and in- 

 consistent; their absence is much more 

 frequent than their presence. 



The operculum has a form very close 

 to that of Hippoporina; we are not posi- 

 FiG. 30— HippopoRiDRA CALCAREA SMITT, tlvely certalu of the presence of museu- 

 ms A. ORDINARY OPERCULUM, X 85. jg^j. attachmeuts. That of the ovicelled 



£. Mandible of an interzooecial . , i • i 



AvicuLARiuM, X 85. c. OPERCULUM OF zooccia IS much wider. 



OVICELLED zooEciuM, X 85 rpj^^ ^^^^ ^f ^^is ovlcell Is uot meffi- 



braneous as Osburn described it in 1914, It is formed by a very 

 fragile olocyst. 



The mandible is star-shaped with three more or less elongated 

 branches. 



Affinities. — The specific differences from Hippoporidra edax Busk, 

 1859, are very slight. We do not yet know the chitinous appendages 

 of the latter species, and we believe it prudent to keep the distinction 

 made by Smitt. Too hasty conclusions as to synonymy are dangerous 

 and lead the paleontologist to false stratigraphic conclusions. 



Hippoporidra calcarea differs from H. maculata Ulrich and Bassler, 

 1904, in which the frontal is without an umbo, in the more acuminate 

 form of the large interzooecial avicularium without a salient beak. 



Biology. — Our colonies encrust gastropods. They emit free radial 

 branches in which the development is in relation to the general 

 equilibrium of the entire colony. They appear to be able to float 



