BRYOZOAN" FAUNA OF VINCENTOWN LIMESAND 55 



Genus KELESTOMA Marsson, 1887 



KELESTOMA SIMPLEX, new species 



Plate 12, Figuke 4 



Description. — The zoarium is encrusting. The zooecia are distinct, 

 separated by a furrow or by " lacunae ", large and variable in form, 

 elliptical, much elongated ; the frontal is convex and formed of 9 to 

 12 wide costules, decorated with pelmatidia, much separated from 

 one another and joined at their extremity with the median longitu- 

 dinal axis; the apertural bar is formed by the first pair of costules 

 absolutely identical with the others. The aperture is semielliptical, 

 invisible, buried at the bottom of a long peristomie ; it is protected 

 by a single convex arch arising from the oral avicularia and attached 

 to the first pair of costules by a median trabecula, which is often 

 perforated. The peristomice (or visible orifice) is semielliptical, 

 transverse, irregular. It is accompanied laterally by two triangular 

 avicularia with a pivot, in which the beak is oriented proximally 

 toward the longitudinal zooecial axis. The ovicell is hyperstomial, 

 not closed by the operculum, opening into the peristomie, very small, 

 little convex, and little visible. 



Measurements . — 



„ . \Lz = 0.75-0.82 mm. _ . , . (A® = 0.12 mm. 

 Zooecia^ , _. _ K Jreristomice{ 7 _ H „ 



I fe=0.35 mm. [lp = 0.15 mm. 



13 zooecia in 4 sq. mm. 



Affinities. — This and the following species belong to the group that 

 Lang, 1922, called Kelestominae and Tricephaloporinae and that the 

 zoologists place in the genus Gephyrotes Norman, 1903. The struc- 

 ture of the frontal arch protecting the aperture has been admirably 

 illustrated by Lang (p. 26, fig. 8). Waters, 1923, 10 confirmed this 

 structure also by an equally good drawing, but he ascribed another 

 origin to it. 



Here the structure is simpler. The arch is attached to the oral 

 avicularia and by a median trabecula to the first pair of costules 

 serving as an apertural bar. In the other species the arch is bifur- 

 cated in the middle with two other attachments on the apertural 

 bar (Waters), or according to Lang, it is the apertural bar that is 

 bifurcated and attached on the median axis to the arch formed by 

 the fusion of two oral spines. 



The protective arch, moreover, is still more complicated in 

 Morphosmopora and often becomes unrecognizable when it is more 

 or less covered by secondary calcification. 



10 Waters, A. W. Mediterranean and other Cribrilinidae. Ann. Mag. Nat. Hist., ser. 

 9, vol. 12, p. 564, pi. 18, figs. 4, 5, 13, 14, 1923. 



