254 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 105 



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Operculum lacking. Zooecial boundaries externally undistinguishable 

 and unmarked. Frontal wall thick, heavily calcified and channeled. 

 Lateral and back walls thin. End wall a porous plate with two cal- 

 careous processes leaning over the plate. Primary orifice wider than 

 long, its proximal border modified or interrupted by an oral ledge. 

 Avicularia of two Idnds, one external, the other internal; both near 

 the orifice, either below or to one side. 



The four previously known species of this genus, all from the Ant- 

 arctic, are Cellarinella duhia Waters 1904, C. foveolata Waters 1904, 

 G. nodulata Waters 1904, and C. watersi Calvet 1909. Since its origi- 

 nal description by Waters in 1904, the genus Cellarinella has been 

 reported only in the papers of Calvet (1909), Thorn ely (1924), and 

 Livingstone (1928) until the present record. 



Levinsen's genus Sclerodomus (1909) has some of the same character- 

 istics as Cellarinella, such as internal avicularium, externally undefin- 

 able zooecial boundaries, a channeled, heavily calcified frontal wall, 

 and porous end wall. Because the 1947-48 collection yielded some 

 intermediate forms it was thought best to retain Waters' names for 

 Cellarinella and Systenopora as well as Levinsen's Sclerodomus but to 

 modify or restrict one of them slightly. During the study of the six 

 species of the 1947-48 collection the problem arose whether a new 

 genus was needed to accommodate those species whose colonies formed 

 heavy, bilaminate, fan-shaped yet dichotomously branched slabs (C. 

 njegovaiiae, C. roydsi, and C. watersi). C. nutti is intermediate be- 

 tween the heavy slablike species and the spindly or tapelike species 

 (C. duhia, C. foveolata, C. laytoni, C. margueritae, C. nodulata, and 

 C. rossi). However, there were too few fully grown or complete 

 colonies in some of the species to show the amount of possible varia- 

 tion in colony form to warrant erecting a new genus on growth form 

 alone. 



The genus appears to be very homogenous. Dift'erences between 

 species are rather slight insofar as individual zoids are concerned but 

 are sometimes considerable when the zoarial growth habit and general 

 colony appearance are considered. Their zoids show close relation- 

 ship in that all have internal avicularia, external avicularia, frontal 

 oral ledge, sieve plate end wall with two calcareous processes over it, 

 a few rosette plates and numerous single pores definitely placed line- 

 arly in the lateral walls, a thick porous channeled frontal wall, and no 

 visible external zooecial boundaries. 



The orientation of the avicularia, both internal and external, and 

 of the frontal oral ledge were found to be important in distinguishing 

 one species from another. Previous authors have overlooked these 

 characters or else have paid them scant attention; consequently, 

 previously described species need be reexamined for these characters. 



