MUCRONELLA COCCINEA. 373 



Zoopcia shortly ovate, often enlarged and rounded below, 

 distinct, divided by rather deep sutures, depressed below, 

 rising towards the aperture, bordered by a raised line, and 

 punctured round the margin ; surface roughened or gra- 

 nular ; orifice terminal, subcircular, with a central tooth 

 on the lower lip and two lateral denticles; the peristome 

 elevated in front into a prominent mucro, by which the 

 central tooth is partially concealed; marginal spines six; 

 on each side of the orifice an avicularium, with a pointed 

 mandible, which is directed outwards and slightly up- 

 wards. Ooecia globular, recumbent, surface granular, 

 two spines visible on each side, in front of it. 



Primary cell rather smaller than the p. ^^ 



rest, raised, surface smooth ; aper- 

 ture terminal, large, orbicular, with 

 a membranous covering, and about 

 twelve tall marginal spines (wood- 

 cut, fig. 17). 



Colonies forming subcircular, glisten- 

 ing crusts, of an orange-red colour. ^ . ,, 

 ° ' ° Primary cell. 



Var. a {mamillata). Zocecia suberect, 



contracted above, ventricose below; the surface tra- 

 versed by numerous furrows, which radiate from below 

 the mouth to the sides of the cell, usually a line of per- 

 forations round the base ; orifice suborbicular ; the 

 peristome much produced in front and at the sides; two 

 lateral avicularia, erect, the mandible pointing straight 

 upwards. Ooscia globose, sulcate, the avicularia stand- 

 ing erect on each side in front. 



Range of Variation. Apart from the mere superficial 

 layer, the changes to which this species is liable are 



it seems to me that the peristome is more elevated and projects more pro- 

 minently in front than is usual in M. coccinea. I can detect no traces of the 

 three denticles ; but their absence may be due to the condition of the fossil. 

 Considering the amount of variation to which the peristome is liable, we 

 should hardly be justified in treating the difiPerence to which I have just 

 referred as a diagnostic. 



