ART. 21 CYCLOSTOMATOUS BRYOZOA CANU AND BASSLER 81 



shorter and shorter; a certain number aborted (by the disappearance 

 of the polypide), closed by a calcareous pellicule and become the 

 dactylethrae. An examination of the extremity of a branch also 

 reveals the same heteroporoid structure, This feature has been 

 described by D'Orbigny, 1852, and by Gregory, 1899, who have 

 established the family Ciausidae upon it. 



In transverse section the tubes are polygonal, with thickened 

 walls, a little larger toward the peripherj^ Among the large tubes 

 appear smaller tubes irregularly scattered; these are newly formed 

 young tubes whose thin base is thus sectioned. The dactylethrae 

 appear as smaller tubes visible only at the periphery. 



In tangential sections the tubes are polygonal, with thick and 

 adjacent walls but in which the interior is rounded. The dactyl- 

 ethrae are smaller and their interior remains polygonal. 



Affinities. — This is the only species of the Ciausidae in which the 

 peristomes are grouped in circular zones separated by narrower 

 zones of dactylethrae. This simple exterior character is sufficient 

 to distinguish it from other species of the Cretaceous and notably 

 from Clausa heteropora D'Orbigny, 1851, very commonly observed in 

 the Cenomanian of Europe, as well as Clausa cranei, new species. 



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

 (common). 



Cotypes.— Cat. No. 69935, U.S.N.M. 



Genus REPTOCLAUSA D'Orbigny, 1853 



1853. Reptoclausa D'Orbigny, Paldontologie frangaise, Terrain Cretac6, vol. 5, 

 p. 887. 



Based on historic considerations and the right of priority, Gregory 

 in 1897 classified the species of this genus in Idmonea Lamouroux, 

 1821. The zoologists have not yet admitted this classification, which 

 would necessitate a complete rearrangement of the bibliography 

 relative to Idmonea. We have nothing to add to this discussion, and 

 while awaiting a decision on the question as to whether Idmonea was 

 clearly defined we will continue to follow the principle of least change. 

 We will preserve, therefore, D'Orbigny's name for the curious forms 

 herein described. 



The tubes are grouped in idmoneiform fascicles, but the tubes do 

 not have adjacent peristomes. The spaces between the fascicles are 

 of real tubes or aborted. They are ramified on the tubes of the fas- 

 cicles primitively formed and their coalescence engenders new fasci- 

 cles. At the exterior they are visible or invisible, according to the 

 thickness of the tissue. 



