PERGEXSELLA. 
209 
each side of the median ridge. From the median series there 
are offshoots forming ridges down the sides of the branches ; 
the lateral series are alternate, and the apertures are biserial 
or multiserial. 
Type Species. 
Idmonea geniculata^ von Hagenow. Maastrichter Kreide : 
Maastricht. 
Aefixities. 
The interesting Bryozoan on which this genus is founded occurs 
in the Maastricht Chalk, and has been previously assigned to 
Idmonea. It differs from other Idmoiiids by having lateral 
alternate series of apertures continued round on to the reverse 
side, as well as a median series. Fig. 19 shows the relation between 
the two series. But for the lateral series this Bryozoan would be 
a near ally of Retecava carmata (Rom.). The genus resembles- 
Bituhigera in the fact that the apertures of the lateral series are 
not uniserial, but it differs from that genus by the possession of 
a prominent median series and by having more than two rows 
of apertures in the lateral series. 
As it was my ill fate to have to propose the abandonment of 
the genus Pergensia, I take this opportunity of reintroducing 
M. Bergens’ name into the nomenclature of Bryozoa. His name 
could not be associated with a more appropriate species than 
P. geniculata, as it is one of the most remarkable members of 
the fauna near M. Pergens’ home. 
Pergensella geniculata (von Hagenow), 1851. 
Synonymy. 
Retepora elathrata, pars, Goldfuss, 1827. Petref. Germ. vol. i. p. 29, pi. ix. 
figs. 12<?,/. 
Idmonea geniculata, von Hagenow, 1851. Bry. Maastr. Kr. p. 33, pi. iii. fig. 5. 
,, ,, Fade, 1852. Los. Verst. Schanzenb. p. 31. 
,, ,, Winkler, 1864. Musee Teyl. : Cat. Pal. livr. ii. p. 213. 
,, ,, Hamm, 1881. Bry. mastr. Ob. -Sen, p. 32. 
Diagnosis. 
Zoarium with narrow reverse face notched by the extension on 
to it of the lateral ridges. 
p 
