362 ESCHARID^J. 



obliterated, the areolation is indistinct, the spines are 

 wanting. In such specimens the conspicuous feature is 

 the slightly everted and projecting lower lip of the aper- 

 ture, which shows as a strip of brighter white on the dull 

 uniform surface. The mucro is usually, in such cases, 

 very inconspicuous ; but the small bifid denticle is present, 

 and the stumps of the six spines may be traced on the 

 upper margin of the mouth. In this condition M. Peachii 

 is of very frequent occurrence on stones and old shells 

 from deep water. Very grotesque varieties are produced 

 by the growth of the thick granular crust over the primi- 

 tive cell-wall. Two striking examples are represented in 

 Plate L. figs. 4, 5. 



The var. (octodentata} is distinguished by its convex, 

 smooth cells and by the position of the ovicell behind the 

 numerous spines. There are commonly eight, occasion- 

 ally only six ; but, in either case, the whole number show 

 in front of the ooecium. This form bears some resem- 

 blance to the Discopora emucronata, described by Smitt 

 from Spitzbergen; but in the Shetland specimens the 

 mucro is certainly not absent. In other respects the two 

 forms agree, and especially in the position of the ovicell 

 behind the numerous spines. This peculiarity, however, 

 can hardly be accounted of any great importance ; in M. 

 ventricosa the oo3cium is often set very far back, so that 

 the whole four spines are visible in front of it, although 

 commonly only one is to be seen on each side. 



HABITAT. On Laminaria, stones, shells, &c., from tide- 

 marks to deep water (170 fathoms). 



LOCALITIES. Universally distributed on our coasts. 

 Var. labiosa. Belfast Bay, deep water (W. T.) : Guernsey 

 (T. H.). Var. octodentata. Shetland (A. M. N.). 



GEOGRAPHICAL DISTRIBUTION. Roscoff (Joliet) : France, 

 S.W., not common (Fischer) : Greenland (German Pol. 



