4 Annals of the South African Museum. 



where they are slightly worn, are somewhat elongated in a 

 proximal-distal direction. 

 Distribution. Senonian. 



IDMONEID^E. 



GENUS IDMONEA, Lamouroux. 



IDMONEA VIKGULA, d'Orbigny. 

 Plate I., fig. 4. 



1851. Lhuonea virgula, d'Orbigny, Bry. Cret., pi. 631, figs. 15-17. 

 1863. Reptotubigera simplex, de Loriol, Invert. Mt. Sal6ve, p. 127 

 pi. xvi., fig. 3. 



Zoarium of a single zocecium-bearing ridge, without a selvage 

 short (about thrice as long as broad), rapidly becoming broader 

 distally. The only specimen of this species has a flat reverse face, 

 but does not encrust any object. But its general shape and corre- 

 spondence with d'Orbiguy's figure of Idmonea virgula renders it 

 probable that it was originally encrusting some perishable object 

 which has since decayed. This raises the question whether other 

 Idmoneidte with flat or convex reverse faces, such as Crisina 

 marginata, d'Orbigny, in some cases may not have been forms 

 encrusting some object, such as seaweed, which has since 

 perished. 



Distribution. Neocomian and Cenomanian. 



GENUS CRISINA, d'Orbigny. 



The separation of Crisina from allied Idmoneid genera, especially 

 from Retecava, is attended with much difficulty.* The genus is 

 here used as restricted by Gregory,! and distinguished from Tervia 

 and lieticrisina, which Gregory regards as subgenera. Tervia is 

 here considered as equal to Crisina in systematic significance. 

 Crisina thus regarded may be defined as a genus of Idmoneidse, 

 in which the zoarium is erect, and consists of solid branches, which 

 are subcylindhcal or moderately compressed ; the reverse face is 

 well developed, but does not overlie an " axial rod " as in Bctccava; 

 there is no unpaired median nor multiple median series of apertures 

 on the obverse face ; the apertures are in single lateral series, and 

 circular. 



* See W. D. Lang, Geol. Mag., 1907, p. 125. 



t J. W. Gregory, Brit. Mus. Cat. Cret. Bry., 1899, vol. i., pp. 159, 168, and 176. 



