90 PROCEEDINGS OF THE NATIONAL MUSEUM vol.67 



Affinities. — This species differs from SipJiodidymn gracile Lonsdale, 

 1849, in its more slender branches showing only 3 or 4 longitudinal 

 series of tubes and in the presence of noncellular zoarial portions. 



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



Cotypes. —C?ii. No. 69944, U.S.N.M. 



Genus ZONOPORA D'Orbigny, 1854 



ZONOPORA COMPRESSA. new species 



Plate 15, figs. 15-17; Plate 31, fig. 1 



Description. — The zoarium is free, dichotomous; the fronds are 

 rawoh.com'pressed. The peristomes are small, thin,nonsalient, arranged 

 in irregular quincunx, grouped in zones separated by wide areas of 

 mesopores and surrounded by some mesopores. 



Measurements. — Diameter of orifice, 0.10 mm.; diameter of meso- 

 pores, 0.04-0.06 mm.; distance of peristomes, 0.24-0.26 mm.; sepa- 

 ration of peristomes, 0.36-0.40 mm. 



Structure. — The sectioned specimens were accidentally hollow, giv- 

 ing the sections a strange aspect which might make them appear 

 to belong to another genus. However, we have found the usual 

 structure seen in sections of Zonopora. 



The longitudinal section in Zonopora is very difficult to interpret 

 because of the great multiplicity of tubes and of their vesicular walls. 

 Those which we have made are not clear enough to be reproduced, 

 but we have been able to observe the essential characters. 



Affinities. — This is the only species of Zonopora in which the fronds 

 are compressed. 



Occurrence. — Lower Cretaceous (Valangian) : Sainte-Croix, Swit- 

 zerland. 



Cotype.—Csit. No. 69945, U.S.N.M. 



ZONOPORA ARBOREA Koch and Dunker, 1837 



Plate 15, figs. 7-10; Plate 31, figs. 2-4 



1909. Multizonopora arborea Gregory, Catalogue Cretaceous Bryozoa in the 

 British Museum, vol. 2, p. 220, figs. 57-61. (Bibliography and geologic 

 distribution.) 



Measurements. — Diameter of the orifices, 0.08 mm.; diameter of 

 the mesopores, 0.04 mm. 



Structure. — The specimens from Sainte-Croix are large and rough, 

 but they are not multilamellar. The cellular zones are very irregular 

 and quite variable in their extent. The determination by the exterior 

 features alone is always difficult if the observer is not acquainted 

 with all the known variations in such fossils. 



The illustrated sections of this species are those of Pergens, 1889, 

 and of Gregory, 1909. Our specimens from Sainte-Croix were silici- 



