80 



PROCEEDINGS OF THE NATIONAL MUSEUM 



Occurrence. — Lower Cretaceous (Aptian) : Faringdon, England 

 (very rare) . 

 Holotype.—Ceit. No. 69934, U.S.N.M. 



CLAUSA ZONIFERA, new species 



Plate 17, figs. 8-11; Plate 31, fig. 9 



Description. — The zoarium is free, cylindrical, borne upon a slightly 

 expanded base, branching dichotomously in the same plane; the 

 branches are cylindrical, rarely claviform. The peristomes are very 

 thin, nonsalient, grouped in irregular zones, and separated by polyg- 

 onal dactylethrae few 

 in number. The tubes 

 are cylindrical, with 

 peripheral gemmation 

 regularly developed 

 around a central axis 

 and at all heights. The 

 ovicell is unknown. 



Measurements. — D i - 

 ameter of orifice, 0.12 

 mm.; diameter of peri- 

 stome, 0.15 mm. ; diam- 

 eter of large branches, 

 2.50 mm. 



Structure. — Exterior- 

 ly this species has the 

 appearance of a Zono- 

 pora. The grouping of 

 the peristomes in circu- 

 lar zones is a deceptive 

 generic character be- 

 cause it does not al- 

 ways correspond to the 

 same internal struc- 

 ture. It is the same as 

 in the clavulate zoarial 

 form; indeed, in this species we have observed this form, although 

 rarely, and we figure a superb unbranched specimen. 



In longitudinal sections the tubes are cylindrical, recurved at their 

 extremity, more or less long according to their distance from the 

 central axis, and narrowed at their base. Their walls divide in two, 

 engendering thus a new tube. This is the usual method of gemma- 

 tion in the heteroporoids (peripheral) . The peripheral tubes are thus 



Fig. 41. — Clausa zonifera, new species. A. Longitudinal section, 

 X 16. The dactyletiirae are produced by dichotomous branching 

 of the walls (peripheral gemmation). B. Transverse section, 

 X 16. The dispersion of the small tubes among the large ones 

 show that gemmation occurs at all distances from the central 

 axis by regular peripheral dichotomous branching. Lower Cre- 

 taceous (Aptian): Faringdon, England 



