174 MICEOPORID.E. 



MiCROPORA CORIACEAj EspCf. 



Plate XXIII. figs. 5-7. 



Plustra coriacea, Esper, Pflanz. Flustr. pi. vii. fig. 2. 

 DiscopoRA CORIACEA, LamJc. An. s. Vert. ed. 2, ii. 251. 

 MiCROPOKA CORIACEA, Gray, B.M. Had. 115: Smitt, Flor. Bryoz. pt. ii. 13, 



pi. iii. fig. 74. 

 Membranipora CORIACEA, BusJc, B.M. Cat. ii. 57, pi. Ixxiii. figs. 4, 5. 



Zocecia broadly elliptical or rhomboidal ; margin slightly 

 roughened, terminating above on each side in a smooth 

 claviform knob ; area minutely granular and punctate, 

 frequently with a foramen on each side a little below 

 the mouth; orifice broader than long, arched above, 

 lower margin straight, pouting. Occasionally an avicu- 

 larium immediately above the orifice, placed somewhat 

 obliquely, mandible directed upwards. Ooecia large, 

 subimmersed, minutely granular, with a projection or 

 rib in front. 



Range of Variation. The foramina in the front wall are 

 frequently wanting ; but in some colonies they are present 

 on almost every cell, and give a very marked character to 

 the specimen. Occasionally the tuberosities, which form 

 so striking a feature of the species, attain an enormous 

 growth. The avicularia seem to be rarely developed. 

 There is always a projection or callosity on the front of 

 the ovicell ; but it varies considerably in character, being 

 in some cases a massive umbo, in others forming a smooth, 

 thickened area, arched, or rising to a blunt point above, 

 and with a rib-like border, and in others, again, assuming 

 the shape which is represented in Plate XXIII. fig. 7. 



Habitat. On shells, stones, &c., from tide-marks to very 

 deep water. 



Localities, Shetland, under stones between tide-marks ; 



