124 BULLETIN 100, UNITED STATES NATIONAL MUSEUM 



They are clearly developed and deep in species where the proximal 

 border of the opesium is convex. The intensity of calcification of 

 the cryptocyst and the position of the opesiular muscles are the sole 

 causes of these variations. We preserve the genus Ogivalia Jullien, 

 1881, for species absolutely deprived of opesiules. The great regu- 

 larity of the opesium seems to indicate a special arrangement of the 

 opesiular muscles and even their total absence. 



4. The onychocellarium is always falciform; there is only a single 

 membrane. It is dissymmetrical like the zooecia themselves, be- 

 cause the retractor muscles of the polypide are often inserted close to 

 one of the proximal angles of the zooecia and not in the zooecial 

 median axis. 



ONYCHOCELLA SUBSYMMETRICA, new species 



Plate 12, figs. 7, 8 



Description. — The zoarium is flesh colored 



ifjl $cll '~m- 1\ and encrusts nullipores and shells. The 



zooecia are distinct, united by their mural 



rim, hexagonal, very little elongated; the 



mural rim is thick and salient; the crypto- 

 Fig. SO.-Onychocella sub- t ^ flftt &nd d The opesium is 



symmetrica, new species . „. ,. , , ,, 



semielliptical, transverse, very close to the 



A. Operculum X85. B. mura i r i m; the proximal border is somewhat 



Operculum attached to ecto- , ,, , , , , . , ... 



cyst, X85; sole, exterior scle- convex and the two lateral indentations are 



rite; scli, interior sclerite; op, of little depth and almost symmetrical. The 



operculum; ed, ectocyst; opZ, onychocellarium is falciform, a little 



base of fold with two black i on g er than the zooecium; its opesium is 



points - elliptical. 



Measurements. — 



. ;^o = 0.16 mm. Q • [7io = 0.12 mm. 



Opesium B| Zo==0 lg mm Upesium « Uo = 14 _ 18 mm< 



[is = 0.40 mm. 



Zooecium 7 



Us = 0.36 mm. 



Opesium of ony- (ho = 0.20 mm. Onychocel- \Lz = 0.50 mm. 

 chocellarium |Zo = 0.10 mm. larium \lz = 0.22-0.24 mm. 



Structure. — We have succeeded in securing a good opercular prepa- 

 ration. The opercular valve is bordered by a sclerite, little thickened ; 

 it is inserted into another exterior sclerite attached to the ectocyst. 

 The ectocyst which surmounts the opesium is separated by a fold of 

 the entire ectocyst; at the base of the fold are two black points which 

 mark the attachment of the opesiular muscles. This opercular 

 structure is absolutely identical with that of Smittipora as already 

 noted by Levinsen in 1909. 



Affinities. — The micrometric dimensions are intermediate between 

 Onychocella angulosa Reuss, 1847, and OnychoceUa dupliciter Canu 

 and Bassler, 1920. The two opesiular indentations are almost 



