150 
IDilONEA. 
Diagnosis. 
Idmoniidae with the zoarium adnate, of simple or hranehed 
ridges, beside which is a flat, thin selvage. The ridges are 
usually triangular or subtriangular in transverse section. 
Apertures opening in transverse alternate series. 
Type Species. 
Idmonea triquetra, Lamouroiix, 1821. Expos, ^feth. p. 80, 
pi. Ixxix. figs. 13-15. Dathoiiian of France and England. 
11 EM arks. 
In the Catalogue of Jurassic Biyozoa tlie zoarium of Idmniun 
was said to he adnate or erect ; hut further examination of 
the post-Jurassic material leads me to go even further from tlic 
zoological definition of the genus Idmonea than 1 then ventured 
to go. The t}7>e of Idmonea triquetra is veiy well marked, and 
different from the erect forms attributed to Idmonea. I therefor<‘ 
accept Idmonea as originally defined, and accept (TOrhigny’s genus 
Crisina for the later developed and more specialized erect members 
of the family. 
The principal synonyms are Reptotuhigera of d’Orbigny, in 
wliich was included the type species of Idmonea and the Lopholepin 
of Shai’pe {gion von Hagenow), and Reptoclausa, d’Orbigny, which 
is clearly the same as Sharpe’s Idmonea. 
The nearest ally of Idmonea is Cn‘si7ia, which differs by its erect 
habit and the absence of the lateral selvage. Rhalangella agi’ees 
with Idmoyiea in being adnate, but differs in the irregularity of its 
series of peristomes and their usually divergent arrangement. 
Idmonea resembles in structure those species of Prohoscina which, 
like P. radioUtorum, have the apertures in transverse series • but 
in those Prohoscince the apertures are in single series, and not in 
regular alternate series. Specimens such as that represented by 
Fig. 1 on p. 50 suggest that the regularity of such Prohosemee is 
an unessential, secondaiy character. 
1. Idmonea hagenowi (Shai-pe), 1854 {non Ebm., 1840). 
Synonymy. * 
Lopholepis hagenovii, Sharpe, 1854. Sands of Farringdon : Quart. Journ. Geol. 
Soc. vol. X. p. 196, pi. V. fig. 7. 
